Profile of DBI.pm

Filename	/usr/lib/x86_64-linux-gnu/perl5/5.20/DBI.pm
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Line	State ments	Time on line	Calls	Time in subs	Code
1					# $Id$
2					# vim: ts=8:sw=4:et
3					#
4					# Copyright (c) 1994-2012 Tim Bunce Ireland
5					#
6					# See COPYRIGHT section in pod text below for usage and distribution rights.
7					#
8
9					package DBI;
10
11					require 5.008_001;
12
13					BEGIN {
14					our $XS_VERSION = our $VERSION = "1.631"; # ==> ALSO update the version in the pod text below!
15					$VERSION = eval $VERSION;
16					}
17
18					=head1 NAME
19
20					DBI - Database independent interface for Perl
21
22					=head1 SYNOPSIS
23
24					use DBI;
25
26					@driver_names = DBI->available_drivers;
27					%drivers = DBI->installed_drivers;
28					@data_sources = DBI->data_sources($driver_name, \%attr);
29
30					$dbh = DBI->connect($data_source, $username, $auth, \%attr);
31
32					$rv = $dbh->do($statement);
33					$rv = $dbh->do($statement, \%attr);
34					$rv = $dbh->do($statement, \%attr, @bind_values);
35
36					$ary_ref = $dbh->selectall_arrayref($statement);
37					$hash_ref = $dbh->selectall_hashref($statement, $key_field);
38
39					$ary_ref = $dbh->selectcol_arrayref($statement);
40					$ary_ref = $dbh->selectcol_arrayref($statement, \%attr);
41
42					@row_ary = $dbh->selectrow_array($statement);
43					$ary_ref = $dbh->selectrow_arrayref($statement);
44					$hash_ref = $dbh->selectrow_hashref($statement);
45
46					$sth = $dbh->prepare($statement);
47					$sth = $dbh->prepare_cached($statement);
48
49					$rc = $sth->bind_param($p_num, $bind_value);
50					$rc = $sth->bind_param($p_num, $bind_value, $bind_type);
51					$rc = $sth->bind_param($p_num, $bind_value, \%attr);
52
53					$rv = $sth->execute;
54					$rv = $sth->execute(@bind_values);
55					$rv = $sth->execute_array(\%attr, ...);
56
57					$rc = $sth->bind_col($col_num, \$col_variable);
58					$rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
59
60					@row_ary = $sth->fetchrow_array;
61					$ary_ref = $sth->fetchrow_arrayref;
62					$hash_ref = $sth->fetchrow_hashref;
63
64					$ary_ref = $sth->fetchall_arrayref;
65					$ary_ref = $sth->fetchall_arrayref( $slice, $max_rows );
66
67					$hash_ref = $sth->fetchall_hashref( $key_field );
68
69					$rv = $sth->rows;
70
71					$rc = $dbh->begin_work;
72					$rc = $dbh->commit;
73					$rc = $dbh->rollback;
74
75					$quoted_string = $dbh->quote($string);
76
77					$rc = $h->err;
78					$str = $h->errstr;
79					$rv = $h->state;
80
81					$rc = $dbh->disconnect;
82
83					I<The synopsis above only lists the major methods and parameters.>
84
85
86					=head2 GETTING HELP
87
88					=head3 General
89
90					Before asking any questions, reread this document, consult the
91					archives and read the DBI FAQ. The archives are listed
92					at the end of this document and on the DBI home page L<http://dbi.perl.org/support/>
93
94					You might also like to read the Advanced DBI Tutorial at
95					L<http://www.slideshare.net/Tim.Bunce/dbi-advanced-tutorial-2007>
96
97					To help you make the best use of the dbi-users mailing list,
98					and any other lists or forums you may use, I recommend that you read
99					"Getting Answers" by Mike Ash: L<http://mikeash.com/getting_answers.html>.
100
101					=head3 Mailing Lists
102
103					If you have questions about DBI, or DBD driver modules, you can get
104					help from the I<dbi-users@perl.org> mailing list. This is the best way to get
105					help. You don't have to subscribe to the list in order to post, though I'd
106					recommend it. You can get help on subscribing and using the list by emailing
107					I<dbi-users-help@perl.org>.
108
109					Please note that Tim Bunce does not maintain the mailing lists or the
110					web pages (generous volunteers do that). So please don't send mail
111					directly to him; he just doesn't have the time to answer questions
112					personally. The I<dbi-users> mailing list has lots of experienced
113					people who should be able to help you if you need it. If you do email
114					Tim he is very likely to just forward it to the mailing list.
115
116					=head3 Online
117
118					StackOverflow has a DBI tag L<http://stackoverflow.com/questions/tagged/dbi>
119					with over 400 questions.
120
121					The DBI home page at L<http://dbi.perl.org/> and the DBI FAQ
122					at L<http://faq.dbi-support.com/> may be worth a visit.
123					They include links to other resources, but I<are rather out-dated>.
124
125					I don't recommend the DBI cpanforum (at http://www.cpanforum.com/dist/DBI)
126					because relatively few people read it compared with dbi-users@perl.org.
127
128					=head3 Reporting a Bug
129
130					If you think you've found a bug then please read
131					"How to Report Bugs Effectively" by Simon Tatham:
132					L<http://www.chiark.greenend.org.uk/~sgtatham/bugs.html>.
133
134					Your problem is most likely related to the specific DBD driver module you're
135					using. If that's the case then click on the 'Bugs' link on the L<http://metacpan.org>
136					page for your driver. Only submit a bug report against the DBI itself if you're
137					sure that your issue isn't related to the driver you're using.
138
139					=head2 NOTES
140
141					This is the DBI specification that corresponds to DBI version 1.631
142					(see L<DBI::Changes> for details).
143
144					The DBI is evolving at a steady pace, so it's good to check that
145					you have the latest copy.
146
147					The significant user-visible changes in each release are documented
148					in the L<DBI::Changes> module so you can read them by executing
149					C<perldoc DBI::Changes>.
150
151					Some DBI changes require changes in the drivers, but the drivers
152					can take some time to catch up. Newer versions of the DBI have
153					added features that may not yet be supported by the drivers you
154					use. Talk to the authors of your drivers if you need a new feature
155					that is not yet supported.
156
157					Features added after DBI 1.21 (February 2002) are marked in the
158					text with the version number of the DBI release they first appeared in.
159
160					Extensions to the DBI API often use the C<DBIx::*> namespace.
161					See L</Naming Conventions and Name Space>. DBI extension modules
162					can be found at L<https://metacpan.org/search?q=DBIx>. And all modules
163					related to the DBI can be found at L<https://metacpan.org/search?q=DBI>.
164
165					=cut
166
167					# The POD text continues at the end of the file.
168
169					use Carp();
170					use DynaLoader ();
171					use Exporter ();
172
173					BEGIN {
174					@ISA = qw(Exporter DynaLoader);
175
176					# Make some utility functions available if asked for
177					@EXPORT = (); # we export nothing by default
178					@EXPORT_OK = qw(%DBI %DBI_methods hash); # also populated by export_ok_tags:
179					%EXPORT_TAGS = (
180					sql_types => [ qw(
181					SQL_GUID
182					SQL_WLONGVARCHAR
183					SQL_WVARCHAR
184					SQL_WCHAR
185					SQL_BIGINT
186					SQL_BIT
187					SQL_TINYINT
188					SQL_LONGVARBINARY
189					SQL_VARBINARY
190					SQL_BINARY
191					SQL_LONGVARCHAR
192					SQL_UNKNOWN_TYPE
193					SQL_ALL_TYPES
194					SQL_CHAR
195					SQL_NUMERIC
196					SQL_DECIMAL
197					SQL_INTEGER
198					SQL_SMALLINT
199					SQL_FLOAT
200					SQL_REAL
201					SQL_DOUBLE
202					SQL_DATETIME
203					SQL_DATE
204					SQL_INTERVAL
205					SQL_TIME
206					SQL_TIMESTAMP
207					SQL_VARCHAR
208					SQL_BOOLEAN
209					SQL_UDT
210					SQL_UDT_LOCATOR
211					SQL_ROW
212					SQL_REF
213					SQL_BLOB
214					SQL_BLOB_LOCATOR
215					SQL_CLOB
216					SQL_CLOB_LOCATOR
217					SQL_ARRAY
218					SQL_ARRAY_LOCATOR
219					SQL_MULTISET
220					SQL_MULTISET_LOCATOR
221					SQL_TYPE_DATE
222					SQL_TYPE_TIME
223					SQL_TYPE_TIMESTAMP
224					SQL_TYPE_TIME_WITH_TIMEZONE
225					SQL_TYPE_TIMESTAMP_WITH_TIMEZONE
226					SQL_INTERVAL_YEAR
227					SQL_INTERVAL_MONTH
228					SQL_INTERVAL_DAY
229					SQL_INTERVAL_HOUR
230					SQL_INTERVAL_MINUTE
231					SQL_INTERVAL_SECOND
232					SQL_INTERVAL_YEAR_TO_MONTH
233					SQL_INTERVAL_DAY_TO_HOUR
234					SQL_INTERVAL_DAY_TO_MINUTE
235					SQL_INTERVAL_DAY_TO_SECOND
236					SQL_INTERVAL_HOUR_TO_MINUTE
237					SQL_INTERVAL_HOUR_TO_SECOND
238					SQL_INTERVAL_MINUTE_TO_SECOND
239					) ],
240					sql_cursor_types => [ qw(
241					SQL_CURSOR_FORWARD_ONLY
242					SQL_CURSOR_KEYSET_DRIVEN
243					SQL_CURSOR_DYNAMIC
244					SQL_CURSOR_STATIC
245					SQL_CURSOR_TYPE_DEFAULT
246					) ], # for ODBC cursor types
247					utils => [ qw(
248					neat neat_list $neat_maxlen dump_results looks_like_number
249					data_string_diff data_string_desc data_diff sql_type_cast
250					DBIstcf_DISCARD_STRING
251					DBIstcf_STRICT
252					) ],
253					profile => [ qw(
254					dbi_profile dbi_profile_merge dbi_profile_merge_nodes dbi_time
255					) ], # notionally "in" DBI::Profile and normally imported from there
256					);
257
258					$DBI::dbi_debug = 0; # mixture of bit fields and int sub-fields
259					$DBI::neat_maxlen = 1000;
260					$DBI::stderr = 2_000_000_000; # a very round number below 2**31
261
262					# If you get an error here like "Can't find loadable object ..."
263					# then you haven't installed the DBI correctly. Read the README
264					# then install it again.
265					if ( $ENV{DBI_PUREPERL} ) {
266					eval { bootstrap DBI $XS_VERSION } if $ENV{DBI_PUREPERL} == 1;
267					require DBI::PurePerl if $@ or $ENV{DBI_PUREPERL} >= 2;
268					$DBI::PurePerl \|\|= 0; # just to silence "only used once" warnings
269					}
270					else {
271					bootstrap DBI $XS_VERSION;
272					}
273
274					$EXPORT_TAGS{preparse_flags} = [ grep { /^DBIpp_\w\w_/ } keys %{__PACKAGE__."::"} ];
275
276					Exporter::export_ok_tags(keys %EXPORT_TAGS);
277
278					}
279
280					# Alias some handle methods to also be DBI class methods
281					for (qw(trace_msg set_err parse_trace_flag parse_trace_flags)) {
282					no strict;
283					*$_ = \&{"DBD::_::common::$_"};
284					}
285
286					use strict;
287
288					DBI->trace(split /=/, $ENV{DBI_TRACE}, 2) if $ENV{DBI_TRACE};
289
290					$DBI::connect_via \|\|= "connect";
291
292					# check if user wants a persistent database connection ( Apache + mod_perl )
293					if ($INC{'Apache/DBI.pm'} && $ENV{MOD_PERL}) {
294					$DBI::connect_via = "Apache::DBI::connect";
295					DBI->trace_msg("DBI connect via $DBI::connect_via in $INC{'Apache/DBI.pm'}\n");
296					}
297
298					# check for weaken support, used by ChildHandles
299					my $HAS_WEAKEN = eval {
300					require Scalar::Util;
301					# this will croak() if this Scalar::Util doesn't have a working weaken().
302					Scalar::Util::weaken( \my $test ); # same test as in t/72childhandles.t
303					1;
304					};
305
306					%DBI::installed_drh = (); # maps driver names to installed driver handles
307					sub installed_drivers { %DBI::installed_drh }
308					%DBI::installed_methods = (); # XXX undocumented, may change
309					sub installed_methods { %DBI::installed_methods }
310
311					# Setup special DBI dynamic variables. See DBI::var::FETCH for details.
312					# These are dynamically associated with the last handle used.
313					tie $DBI::err, 'DBI::var', '*err'; # special case: referenced via IHA list
314					tie $DBI::state, 'DBI::var', '"state'; # special case: referenced via IHA list
315					tie $DBI::lasth, 'DBI::var', '!lasth'; # special case: return boolean
316					tie $DBI::errstr, 'DBI::var', '&errstr'; # call &errstr in last used pkg
317					tie $DBI::rows, 'DBI::var', '&rows'; # call &rows in last used pkg
318					sub DBI::var::TIESCALAR{ my $var = $_[1]; bless \$var, 'DBI::var'; }
319					sub DBI::var::STORE { Carp::croak("Can't modify \$DBI::${$_[0]} special variable") }
320
321					# --- Driver Specific Prefix Registry ---
322
323					my $dbd_prefix_registry = {
324					ad_ => { class => 'DBD::AnyData', },
325					ado_ => { class => 'DBD::ADO', },
326					amzn_ => { class => 'DBD::Amazon', },
327					best_ => { class => 'DBD::BestWins', },
328					csv_ => { class => 'DBD::CSV', },
329					cubrid_ => { class => 'DBD::cubrid', },
330					db2_ => { class => 'DBD::DB2', },
331					dbi_ => { class => 'DBI', },
332					dbm_ => { class => 'DBD::DBM', },
333					df_ => { class => 'DBD::DF', },
334					examplep_ => { class => 'DBD::ExampleP', },
335					f_ => { class => 'DBD::File', },
336					file_ => { class => 'DBD::TextFile', },
337					go_ => { class => 'DBD::Gofer', },
338					ib_ => { class => 'DBD::InterBase', },
339					ing_ => { class => 'DBD::Ingres', },
340					ix_ => { class => 'DBD::Informix', },
341					jdbc_ => { class => 'DBD::JDBC', },
342					mo_ => { class => 'DBD::MO', },
343					monetdb_ => { class => 'DBD::monetdb', },
344					msql_ => { class => 'DBD::mSQL', },
345					mvsftp_ => { class => 'DBD::MVS_FTPSQL', },
346					mysql_ => { class => 'DBD::mysql', },
347					mx_ => { class => 'DBD::Multiplex', },
348					nullp_ => { class => 'DBD::NullP', },
349					odbc_ => { class => 'DBD::ODBC', },
350					ora_ => { class => 'DBD::Oracle', },
351					pg_ => { class => 'DBD::Pg', },
352					pgpp_ => { class => 'DBD::PgPP', },
353					plb_ => { class => 'DBD::Plibdata', },
354					po_ => { class => 'DBD::PO', },
355					proxy_ => { class => 'DBD::Proxy', },
356					ram_ => { class => 'DBD::RAM', },
357					rdb_ => { class => 'DBD::RDB', },
358					sapdb_ => { class => 'DBD::SAP_DB', },
359					snmp_ => { class => 'DBD::SNMP', },
360					solid_ => { class => 'DBD::Solid', },
361					spatialite_ => { class => 'DBD::Spatialite', },
362					sponge_ => { class => 'DBD::Sponge', },
363					sql_ => { class => 'DBI::DBD::SqlEngine', },
364					sqlite_ => { class => 'DBD::SQLite', },
365					syb_ => { class => 'DBD::Sybase', },
366					sys_ => { class => 'DBD::Sys', },
367					tdat_ => { class => 'DBD::Teradata', },
368					tmpl_ => { class => 'DBD::Template', },
369					tmplss_ => { class => 'DBD::TemplateSS', },
370					tree_ => { class => 'DBD::TreeData', },
371					tuber_ => { class => 'DBD::Tuber', },
372					uni_ => { class => 'DBD::Unify', },
373					vt_ => { class => 'DBD::Vt', },
374					wmi_ => { class => 'DBD::WMI', },
375					x_ => { }, # for private use
376					xbase_ => { class => 'DBD::XBase', },
377					xl_ => { class => 'DBD::Excel', },
378					yaswi_ => { class => 'DBD::Yaswi', },
379					};
380
381					my %dbd_class_registry = map { $dbd_prefix_registry->{$_}->{class} => { prefix => $_ } }
382					grep { exists $dbd_prefix_registry->{$_}->{class} }
383					keys %{$dbd_prefix_registry};
384
385					sub dump_dbd_registry {
386					require Data::Dumper;
387					local $Data::Dumper::Sortkeys=1;
388					local $Data::Dumper::Indent=1;
389					print Data::Dumper->Dump([$dbd_prefix_registry], [qw($dbd_prefix_registry)]);
390					}
391
392					# --- Dynamically create the DBI Standard Interface
393
394					my $keeperr = { O=>0x0004 };
395
396					%DBI::DBI_methods = ( # Define the DBI interface methods per class:
397
398					common => { # Interface methods common to all DBI handle classes
399					'DESTROY' => { O=>0x004\|0x10000 },
400					'CLEAR' => $keeperr,
401					'EXISTS' => $keeperr,
402					'FETCH' => { O=>0x0404 },
403					'FETCH_many' => { O=>0x0404 },
404					'FIRSTKEY' => $keeperr,
405					'NEXTKEY' => $keeperr,
406					'STORE' => { O=>0x0418 \| 0x4 },
407					can => { O=>0x0100 }, # special case, see dispatch
408					debug => { U =>[1,2,'[$debug_level]'], O=>0x0004 }, # old name for trace
409					dump_handle => { U =>[1,3,'[$message [, $level]]'], O=>0x0004 },
410					err => $keeperr,
411					errstr => $keeperr,
412					state => $keeperr,
413					func => { O=>0x0006 },
414					parse_trace_flag => { U =>[2,2,'$name'], O=>0x0404, T=>8 },
415					parse_trace_flags => { U =>[2,2,'$flags'], O=>0x0404, T=>8 },
416					private_data => { U =>[1,1], O=>0x0004 },
417					set_err => { U =>[3,6,'$err, $errmsg [, $state, $method, $rv]'], O=>0x0010 },
418					trace => { U =>[1,3,'[$trace_level, [$filename]]'], O=>0x0004 },
419					trace_msg => { U =>[2,3,'$message_text [, $min_level ]' ], O=>0x0004, T=>8 },
420					swap_inner_handle => { U =>[2,3,'$h [, $allow_reparent ]'] },
421					private_attribute_info => { },
422					visit_child_handles => { U => [2,3,'$coderef [, $info ]'], O=>0x0404, T=>4 },
423					},
424					dr => { # Database Driver Interface
425					'connect' => { U =>[1,5,'[$db [,$user [,$passwd [,\%attr]]]]'], H=>3, O=>0x8000, T=>0x200 },
426					'connect_cached'=>{U=>[1,5,'[$db [,$user [,$passwd [,\%attr]]]]'], H=>3, O=>0x8000, T=>0x200 },
427					'disconnect_all'=>{ U =>[1,1], O=>0x0800, T=>0x200 },
428					data_sources => { U =>[1,2,'[\%attr]' ], O=>0x0800, T=>0x200 },
429					default_user => { U =>[3,4,'$user, $pass [, \%attr]' ], T=>0x200 },
430					dbixs_revision => $keeperr,
431					},
432					db => { # Database Session Class Interface
433					data_sources => { U =>[1,2,'[\%attr]' ], O=>0x0200 },
434					take_imp_data => { U =>[1,1], O=>0x10000 },
435					clone => { U =>[1,2,'[\%attr]'], T=>0x200 },
436					connected => { U =>[1,0], O => 0x0004, T=>0x200, H=>3 },
437					begin_work => { U =>[1,2,'[ \%attr ]'], O=>0x0400, T=>0x1000 },
438					commit => { U =>[1,1], O=>0x0480\|0x0800, T=>0x1000 },
439					rollback => { U =>[1,1], O=>0x0480\|0x0800, T=>0x1000 },
440					'do' => { U =>[2,0,'$statement [, \%attr [, @bind_params ] ]'], O=>0x3200 },
441					last_insert_id => { U =>[5,6,'$catalog, $schema, $table_name, $field_name [, \%attr ]'], O=>0x2800 },
442					preparse => { }, # XXX
443					prepare => { U =>[2,3,'$statement [, \%attr]'], O=>0xA200 },
444					prepare_cached => { U =>[2,4,'$statement [, \%attr [, $if_active ] ]'], O=>0xA200 },
445					selectrow_array => { U =>[2,0,'$statement [, \%attr [, @bind_params ] ]'], O=>0x2000 },
446					selectrow_arrayref=>{U =>[2,0,'$statement [, \%attr [, @bind_params ] ]'], O=>0x2000 },
447					selectrow_hashref=>{ U =>[2,0,'$statement [, \%attr [, @bind_params ] ]'], O=>0x2000 },
448					selectall_arrayref=>{U =>[2,0,'$statement [, \%attr [, @bind_params ] ]'], O=>0x2000 },
449					selectall_hashref=>{ U =>[3,0,'$statement, $keyfield [, \%attr [, @bind_params ] ]'], O=>0x2000 },
450					selectcol_arrayref=>{U =>[2,0,'$statement [, \%attr [, @bind_params ] ]'], O=>0x2000 },
451					ping => { U =>[1,1], O=>0x0404 },
452					disconnect => { U =>[1,1], O=>0x0400\|0x0800\|0x10000, T=>0x200 },
453					quote => { U =>[2,3, '$string [, $data_type ]' ], O=>0x0430, T=>2 },
454					quote_identifier=> { U =>[2,6, '$name [, ...] [, \%attr ]' ], O=>0x0430, T=>2 },
455					rows => $keeperr,
456
457					tables => { U =>[1,6,'$catalog, $schema, $table, $type [, \%attr ]' ], O=>0x2200 },
458					table_info => { U =>[1,6,'$catalog, $schema, $table, $type [, \%attr ]' ], O=>0x2200\|0x8800 },
459					column_info => { U =>[5,6,'$catalog, $schema, $table, $column [, \%attr ]'],O=>0x2200\|0x8800 },
460					primary_key_info=> { U =>[4,5,'$catalog, $schema, $table [, \%attr ]' ], O=>0x2200\|0x8800 },
461					primary_key => { U =>[4,5,'$catalog, $schema, $table [, \%attr ]' ], O=>0x2200 },
462					foreign_key_info=> { U =>[7,8,'$pk_catalog, $pk_schema, $pk_table, $fk_catalog, $fk_schema, $fk_table [, \%attr ]' ], O=>0x2200\|0x8800 },
463					statistics_info => { U =>[6,7,'$catalog, $schema, $table, $unique_only, $quick, [, \%attr ]' ], O=>0x2200\|0x8800 },
464					type_info_all => { U =>[1,1], O=>0x2200\|0x0800 },
465					type_info => { U =>[1,2,'$data_type'], O=>0x2200 },
466					get_info => { U =>[2,2,'$info_type'], O=>0x2200\|0x0800 },
467					},
468					st => { # Statement Class Interface
469					bind_col => { U =>[3,4,'$column, \\$var [, \%attr]'] },
470					bind_columns => { U =>[2,0,'\\$var1 [, \\$var2, ...]'] },
471					bind_param => { U =>[3,4,'$parameter, $var [, \%attr]'] },
472					bind_param_inout=> { U =>[4,5,'$parameter, \\$var, $maxlen, [, \%attr]'] },
473					execute => { U =>[1,0,'[@args]'], O=>0x1040 },
474
475					bind_param_array => { U =>[3,4,'$parameter, $var [, \%attr]'] },
476					bind_param_inout_array => { U =>[4,5,'$parameter, \\@var, $maxlen, [, \%attr]'] },
477					execute_array => { U =>[2,0,'\\%attribs [, @args]'], O=>0x1040\|0x4000 },
478					execute_for_fetch => { U =>[2,3,'$fetch_sub [, $tuple_status]'], O=>0x1040\|0x4000 },
479
480					fetch => undef, # alias for fetchrow_arrayref
481					fetchrow_arrayref => undef,
482					fetchrow_hashref => undef,
483					fetchrow_array => undef,
484					fetchrow => undef, # old alias for fetchrow_array
485
486					fetchall_arrayref => { U =>[1,3, '[ $slice [, $max_rows]]'] },
487					fetchall_hashref => { U =>[2,2,'$key_field'] },
488
489					blob_read => { U =>[4,5,'$field, $offset, $len [, \\$buf [, $bufoffset]]'] },
490					blob_copy_to_file => { U =>[3,3,'$field, $filename_or_handleref'] },
491					dump_results => { U =>[1,5,'$maxfieldlen, $linesep, $fieldsep, $filehandle'] },
492					more_results => { U =>[1,1] },
493					finish => { U =>[1,1] },
494					cancel => { U =>[1,1], O=>0x0800 },
495					rows => $keeperr,
496
497					_get_fbav => undef,
498					_set_fbav => { T=>6 },
499					},
500					);
501
502					while ( my ($class, $meths) = each %DBI::DBI_methods ) {
503					my $ima_trace = 0+($ENV{DBI_IMA_TRACE}\|\|0);
504					while ( my ($method, $info) = each %$meths ) {
505					my $fullmeth = "DBI::${class}::$method";
506					if (($DBI::dbi_debug & 0xF) == 15) { # quick hack to list DBI methods
507					# and optionally filter by IMA flags
508					my $O = $info->{O}\|\|0;
509					printf "0x%04x %-20s\n", $O, $fullmeth
510					unless $ima_trace && !($O & $ima_trace);
511					}
512					DBI->_install_method($fullmeth, 'DBI.pm', $info);
513					}
514					}
515
516					{
517					package DBI::common;
518					@DBI::dr::ISA = ('DBI::common');
519					@DBI::db::ISA = ('DBI::common');
520					@DBI::st::ISA = ('DBI::common');
521					}
522
523					# End of init code
524
525
526					END {
527					return unless defined &DBI::trace_msg; # return unless bootstrap'd ok
528					local ($!,$?);
529					DBI->trace_msg(sprintf(" -- DBI::END (\$\@: %s, \$!: %s)\n", $@\|\|'', $!\|\|''), 2);
530					# Let drivers know why we are calling disconnect_all:
531					$DBI::PERL_ENDING = $DBI::PERL_ENDING = 1; # avoid typo warning
532					DBI->disconnect_all() if %DBI::installed_drh;
533					}
534
535
536					sub CLONE {
537					_clone_dbis() unless $DBI::PurePerl; # clone the DBIS structure
538					DBI->trace_msg("CLONE DBI for new thread\n");
539					while ( my ($driver, $drh) = each %DBI::installed_drh) {
540					no strict 'refs';
541					next if defined &{"DBD::${driver}::CLONE"};
542					warn("$driver has no driver CLONE() function so is unsafe threaded\n");
543					}
544					%DBI::installed_drh = (); # clear loaded drivers so they have a chance to reinitialize
545					}
546
547					sub parse_dsn {
548					my ($class, $dsn) = @_;
549					$dsn =~ s/^(dbi):(\w?)(?:$(.?)$)?://i or return;
550					my ($scheme, $driver, $attr, $attr_hash) = (lc($1), $2, $3);
551					$driver \|\|= $ENV{DBI_DRIVER} \|\| '';
552					$attr_hash = { split /\s=>?\s\|\s,\s/, $attr, -1 } if $attr;
553					return ($scheme, $driver, $attr, $attr_hash, $dsn);
554					}
555
556					sub visit_handles {
557					my ($class, $code, $outer_info) = @_;
558					$outer_info = {} if not defined $outer_info;
559					my %drh = DBI->installed_drivers;
560					for my $h (values %drh) {
561					my $child_info = $code->($h, $outer_info)
562					or next;
563					$h->visit_child_handles($code, $child_info);
564					}
565					return $outer_info;
566					}
567
568
569					# --- The DBI->connect Front Door methods
570
571					sub connect_cached {
572					# For library code using connect_cached() with mod_perl
573					# we redirect those calls to Apache::DBI::connect() as well
574					my ($class, $dsn, $user, $pass, $attr) = @_;
575					my $dbi_connect_method = ($DBI::connect_via eq "Apache::DBI::connect")
576					? 'Apache::DBI::connect' : 'connect_cached';
577					$attr = {
578					$attr ? %$attr : (), # clone, don't modify callers data
579					dbi_connect_method => $dbi_connect_method,
580					};
581					return $class->connect($dsn, $user, $pass, $attr);
582					}
583
584					sub connect {
585					my $class = shift;
586					my ($dsn, $user, $pass, $attr, $old_driver) = my @orig_args = @_;
587					my $driver;
588
589					if ($attr and !ref($attr)) { # switch $old_driver<->$attr if called in old style
590					Carp::carp("DBI->connect using 'old-style' syntax is deprecated and will be an error in future versions");
591					($old_driver, $attr) = ($attr, $old_driver);
592					}
593
594					my $connect_meth = $attr->{dbi_connect_method};
595					$connect_meth \|\|= $DBI::connect_via; # fallback to default
596
597					$dsn \|\|= $ENV{DBI_DSN} \|\| $ENV{DBI_DBNAME} \|\| '' unless $old_driver;
598
599					if ($DBI::dbi_debug) {
600					local $^W = 0;
601					pop @_ if $connect_meth ne 'connect';
602					my @args = @_; $args[2] = '****'; # hide password
603					DBI->trace_msg(" -> $class->$connect_meth(".join(", ",@args).")\n");
604					}
605					Carp::croak('Usage: $class->connect([$dsn [,$user [,$passwd [,\%attr]]]])')
606					if (ref $old_driver or ($attr and not ref $attr) or ref $pass);
607
608					# extract dbi:driver prefix from $dsn into $1
609					$dsn =~ s/^dbi:(\w?)(?:$(.?)$)?://i
610					or '' =~ /()/; # ensure $1 etc are empty if match fails
611					my $driver_attrib_spec = $2 \|\| '';
612
613					# Set $driver. Old style driver, if specified, overrides new dsn style.
614					$driver = $old_driver \|\| $1 \|\| $ENV{DBI_DRIVER}
615					or Carp::croak("Can't connect to data source '$dsn' "
616					."because I can't work out what driver to use "
617					."(it doesn't seem to contain a 'dbi:driver:' prefix "
618					."and the DBI_DRIVER env var is not set)");
619
620					my $proxy;
621					if ($ENV{DBI_AUTOPROXY} && $driver ne 'Proxy' && $driver ne 'Sponge' && $driver ne 'Switch') {
622					my $dbi_autoproxy = $ENV{DBI_AUTOPROXY};
623					$proxy = 'Proxy';
624					if ($dbi_autoproxy =~ s/^dbi:(\w?)(?:$(.?)$)?://i) {
625					$proxy = $1;
626					$driver_attrib_spec = join ",",
627					($driver_attrib_spec) ? $driver_attrib_spec : (),
628					($2 ) ? $2 : ();
629					}
630					$dsn = "$dbi_autoproxy;dsn=dbi:$driver:$dsn";
631					$driver = $proxy;
632					DBI->trace_msg(" DBI_AUTOPROXY: dbi:$driver($driver_attrib_spec):$dsn\n");
633					}
634					# avoid recursion if proxy calls DBI->connect itself
635					local $ENV{DBI_AUTOPROXY} if $ENV{DBI_AUTOPROXY};
636
637					my %attributes; # take a copy we can delete from
638					if ($old_driver) {
639					%attributes = %$attr if $attr;
640					}
641					else { # new-style connect so new default semantics
642					%attributes = (
643					PrintError => 1,
644					AutoCommit => 1,
645					ref $attr ? %$attr : (),
646					# attributes in DSN take precedence over \%attr connect parameter
647					$driver_attrib_spec ? (split /\s=>?\s\|\s,\s/, $driver_attrib_spec, -1) : (),
648					);
649					}
650					$attr = \%attributes; # now set $attr to refer to our local copy
651
652					my $drh = $DBI::installed_drh{$driver} \|\| $class->install_driver($driver)
653					or die "panic: $class->install_driver($driver) failed";
654
655					# attributes in DSN take precedence over \%attr connect parameter
656					$user = $attr->{Username} if defined $attr->{Username};
657					$pass = $attr->{Password} if defined $attr->{Password};
658					delete $attr->{Password}; # always delete Password as closure stores it securely
659					if ( !(defined $user && defined $pass) ) {
660					($user, $pass) = $drh->default_user($user, $pass, $attr);
661					}
662					$attr->{Username} = $user; # force the Username to be the actual one used
663
664					my $connect_closure = sub {
665					my ($old_dbh, $override_attr) = @_;
666
667					#use Data::Dumper;
668					#warn "connect_closure: ".Data::Dumper::Dumper([$attr,\%attributes, $override_attr]);
669
670					my $dbh;
671	1	81µs	1	1.81ms	unless ($dbh = $drh->$connect_meth($dsn, $user, $pass, $attr)) { # spent 1.81ms making 1 call to DBD::mysql::dr::connect
672					$user = '' if !defined $user;
673					$dsn = '' if !defined $dsn;
674					# $drh->errstr isn't safe here because $dbh->DESTROY may not have
675					# been called yet and so the dbh errstr would not have been copied
676					# up to the drh errstr. Certainly true for connect_cached!
677					my $errstr = $DBI::errstr;
678					# Getting '(no error string)' here is a symptom of a ref loop
679					$errstr = '(no error string)' if !defined $errstr;
680					my $msg = "$class connect('$dsn','$user',...) failed: $errstr";
681					DBI->trace_msg(" $msg\n");
682					# XXX HandleWarn
683					unless ($attr->{HandleError} && $attr->{HandleError}->($msg, $drh, $dbh)) {
684					Carp::croak($msg) if $attr->{RaiseError};
685					Carp::carp ($msg) if $attr->{PrintError};
686					}
687					$! = 0; # for the daft people who do DBI->connect(...) \|\| die "$!";
688					return $dbh; # normally undef, but HandleError could change it
689					}
690
691					# merge any attribute overrides but don't change $attr itself (for closure)
692					my $apply = { ($override_attr) ? (%$attr, %$override_attr ) : %$attr };
693
694					# handle basic RootClass subclassing:
695					my $rebless_class = $apply->{RootClass} \|\| ($class ne 'DBI' ? $class : '');
696					if ($rebless_class) {
697					no strict 'refs';
698					if ($apply->{RootClass}) { # explicit attribute (ie not static method call class)
699					delete $apply->{RootClass};
700					DBI::_load_class($rebless_class, 0);
701					}
702					unless (@{"$rebless_class\::db::ISA"} && @{"$rebless_class\::st::ISA"}) {
703					Carp::carp("DBI subclasses '$rebless_class\::db' and ::st are not setup, RootClass ignored");
704					$rebless_class = undef;
705					$class = 'DBI';
706					}
707					else {
708					$dbh->{RootClass} = $rebless_class; # $dbh->STORE called via plain DBI::db
709					DBI::_set_isa([$rebless_class], 'DBI'); # sets up both '::db' and '::st'
710					DBI::_rebless($dbh, $rebless_class); # appends '::db'
711					}
712					}
713
714					if (%$apply) {
715
716					if ($apply->{DbTypeSubclass}) {
717					my $DbTypeSubclass = delete $apply->{DbTypeSubclass};
718					DBI::_rebless_dbtype_subclass($dbh, $rebless_class\|\|$class, $DbTypeSubclass);
719					}
720					my $a;
721					foreach $a (qw(Profile RaiseError PrintError AutoCommit)) { # do these first
722					next unless exists $apply->{$a};
723			3	7µs	$dbh->{$a} = delete $apply->{$a}; # spent 7µs making 3 calls to DBI::common::STORE, avg 2µs/call
724					}
725					while ( my ($a, $v) = each %$apply) {
726			3	5µs	eval { $dbh->{$a} = $v }; # assign in void context to avoid re-FETCH # spent 5µs making 3 calls to DBI::common::STORE, avg 2µs/call
727					warn $@ if $@;
728					}
729					}
730
731					# confirm to driver (ie if subclassed) that we've connected successfully
732					# and finished the attribute setup. pass in the original arguments
733					$dbh->connected(@orig_args); #if ref $dbh ne 'DBI::db' or $proxy;
734
735					DBI->trace_msg(" <- connect= $dbh\n") if $DBI::dbi_debug & 0xF;
736
737					return $dbh;
738					};
739
740					my $dbh = &$connect_closure(undef, undef);
741
742			1	5µs	$dbh->{dbi_connect_closure} = $connect_closure if $dbh; # spent 5µs making 1 call to DBI::common::STORE
743
744					return $dbh;
745					}
746
747
748					sub disconnect_all {
749					keys %DBI::installed_drh; # reset iterator
750					while ( my ($name, $drh) = each %DBI::installed_drh ) {
751					$drh->disconnect_all() if ref $drh;
752					}
753					}
754
755
756					sub disconnect { # a regular beginners bug
757					Carp::croak("DBI->disconnect is not a DBI method (read the DBI manual)");
758					}
759
760
761					sub install_driver { # croaks on failure
762					my $class = shift;
763					my($driver, $attr) = @_;
764					my $drh;
765
766					$driver \|\|= $ENV{DBI_DRIVER} \|\| '';
767
768					# allow driver to be specified as a 'dbi:driver:' string
769					$driver = $1 if $driver =~ s/^DBI:(.*?)://i;
770
771					Carp::croak("usage: $class->install_driver(\$driver [, \%attr])")
772					unless ($driver and @_<=3);
773
774					# already installed
775					return $drh if $drh = $DBI::installed_drh{$driver};
776
777					$class->trace_msg(" -> $class->install_driver($driver"
778					.") for $^O perl=$] pid=$$ ruid=$< euid=$>\n")
779					if $DBI::dbi_debug & 0xF;
780
781					# --- load the code
782					my $driver_class = "DBD::$driver";
783	1	119µs			eval qq{package # hide from PAUSE # spent 164µs executing statements in string eval
784					DBI::_firesafe; # just in case
785					require $driver_class; # load the driver
786					};
787					if ($@) {
788					my $err = $@;
789					my $advice = "";
790					if ($err =~ /Can't find loadable object/) {
791					$advice = "Perhaps DBD::$driver was statically linked into a new perl binary."
792					."\nIn which case you need to use that new perl binary."
793					."\nOr perhaps only the .pm file was installed but not the shared object file."
794					}
795					elsif ($err =~ /Can't locate.*?DBD\/$driver\.pm in \@INC/) {
796					my @drv = $class->available_drivers(1);
797					$advice = "Perhaps the DBD::$driver perl module hasn't been fully installed,\n"
798					."or perhaps the capitalisation of '$driver' isn't right.\n"
799					."Available drivers: ".join(", ", @drv).".";
800					}
801					elsif ($err =~ /Can't load .*? for module DBD::/) {
802					$advice = "Perhaps a required shared library or dll isn't installed where expected";
803					}
804					elsif ($err =~ /Can't locate .*? in \@INC/) {
805					$advice = "Perhaps a module that DBD::$driver requires hasn't been fully installed";
806					}
807					Carp::croak("install_driver($driver) failed: $err$advice\n");
808					}
809					if ($DBI::dbi_debug & 0xF) {
810					no strict 'refs';
811					(my $driver_file = $driver_class) =~ s/::/\//g;
812					my $dbd_ver = ${"$driver_class\::VERSION"} \|\| "undef";
813					$class->trace_msg(" install_driver: $driver_class version $dbd_ver"
814					." loaded from $INC{qq($driver_file.pm)}\n");
815					}
816
817					# --- do some behind-the-scenes checks and setups on the driver
818					$class->setup_driver($driver_class);
819
820					# --- run the driver function
821	1	37µs			$drh = eval { $driver_class->driver($attr \|\| {}) };
822					unless ($drh && ref $drh && !$@) {
823					my $advice = "";
824					$@ \|\|= "$driver_class->driver didn't return a handle";
825					# catch people on case in-sensitive systems using the wrong case
826					$advice = "\nPerhaps the capitalisation of DBD '$driver' isn't right."
827					if $@ =~ /locate object method/;
828					Carp::croak("$driver_class initialisation failed: $@$advice");
829					}
830
831					$DBI::installed_drh{$driver} = $drh;
832					$class->trace_msg(" <- install_driver= $drh\n") if $DBI::dbi_debug & 0xF;
833					$drh;
834					}
835
836					*driver = \&install_driver; # currently an alias, may change
837
838
839					sub setup_driver {
840					my ($class, $driver_class) = @_;
841					my $h_type;
842					foreach $h_type (qw(dr db st)){
843					my $h_class = $driver_class."::$h_type";
844					no strict 'refs';
845					push @{"${h_class}::ISA"}, "DBD::_::$h_type"
846					unless UNIVERSAL::isa($h_class, "DBD::_::$h_type");
847					# The _mem class stuff is (IIRC) a crufty hack for global destruction
848					# timing issues in early versions of perl5 and possibly no longer needed.
849					my $mem_class = "DBD::_mem::$h_type";
850					push @{"${h_class}_mem::ISA"}, $mem_class
851					unless UNIVERSAL::isa("${h_class}_mem", $mem_class)
852					or $DBI::PurePerl;
853					}
854					}
855
856
857					sub _rebless {
858					my $dbh = shift;
859					my ($outer, $inner) = DBI::_handles($dbh);
860					my $class = shift(@_).'::db';
861					bless $inner => $class;
862					bless $outer => $class; # outer last for return
863					}
864
865
866					sub _set_isa {
867					my ($classes, $topclass) = @_;
868					my $trace = DBI->trace_msg(" _set_isa([@$classes])\n");
869					foreach my $suffix ('::db','::st') {
870					my $previous = $topclass \|\| 'DBI'; # trees are rooted here
871					foreach my $class (@$classes) {
872					my $base_class = $previous.$suffix;
873					my $sub_class = $class.$suffix;
874					my $sub_class_isa = "${sub_class}::ISA";
875					no strict 'refs';
876					if (@$sub_class_isa) {
877					DBI->trace_msg(" $sub_class_isa skipped (already set to @$sub_class_isa)\n")
878					if $trace;
879					}
880					else {
881					@$sub_class_isa = ($base_class) unless @$sub_class_isa;
882					DBI->trace_msg(" $sub_class_isa = $base_class\n")
883					if $trace;
884					}
885					$previous = $class;
886					}
887					}
888					}
889
890
891					sub _rebless_dbtype_subclass {
892					my ($dbh, $rootclass, $DbTypeSubclass) = @_;
893					# determine the db type names for class hierarchy
894					my @hierarchy = DBI::_dbtype_names($dbh, $DbTypeSubclass);
895					# add the rootclass prefix to each ('DBI::' or 'MyDBI::' etc)
896					$_ = $rootclass.'::'.$_ foreach (@hierarchy);
897					# load the modules from the 'top down'
898					DBI::_load_class($_, 1) foreach (reverse @hierarchy);
899					# setup class hierarchy if needed, does both '::db' and '::st'
900					DBI::_set_isa(\@hierarchy, $rootclass);
901					# finally bless the handle into the subclass
902					DBI::_rebless($dbh, $hierarchy[0]);
903					}
904
905
906					sub _dbtype_names { # list dbtypes for hierarchy, ie Informix=>ADO=>ODBC
907					my ($dbh, $DbTypeSubclass) = @_;
908
909					if ($DbTypeSubclass && $DbTypeSubclass ne '1' && ref $DbTypeSubclass ne 'CODE') {
910					# treat $DbTypeSubclass as a comma separated list of names
911					my @dbtypes = split /\s,\s/, $DbTypeSubclass;
912					$dbh->trace_msg(" DbTypeSubclass($DbTypeSubclass)=@dbtypes (explicit)\n");
913					return @dbtypes;
914					}
915
916					# XXX will call $dbh->get_info(17) (=SQL_DBMS_NAME) in future?
917
918					my $driver = $dbh->{Driver}->{Name};
919					if ( $driver eq 'Proxy' ) {
920					# XXX Looking into the internals of DBD::Proxy is questionable!
921					($driver) = $dbh->{proxy_client}->{application} =~ /^DBI:(.+?):/i
922					or die "Can't determine driver name from proxy";
923					}
924
925					my @dbtypes = (ucfirst($driver));
926					if ($driver eq 'ODBC' \|\| $driver eq 'ADO') {
927					# XXX will move these out and make extensible later:
928					my $_dbtype_name_regexp = 'Oracle'; # eg 'Oracle\|Foo\|Bar'
929					my %_dbtype_name_map = (
930					'Microsoft SQL Server' => 'MSSQL',
931					'SQL Server' => 'Sybase',
932					'Adaptive Server Anywhere' => 'ASAny',
933					'ADABAS D' => 'AdabasD',
934					);
935
936					my $name;
937					$name = $dbh->func(17, 'GetInfo') # SQL_DBMS_NAME
938					if $driver eq 'ODBC';
939					$name = $dbh->{ado_conn}->Properties->Item('DBMS Name')->Value
940					if $driver eq 'ADO';
941					die "Can't determine driver name! ($DBI::errstr)\n"
942					unless $name;
943
944					my $dbtype;
945					if ($_dbtype_name_map{$name}) {
946					$dbtype = $_dbtype_name_map{$name};
947					}
948					else {
949					if ($name =~ /($_dbtype_name_regexp)/) {
950					$dbtype = lc($1);
951					}
952					else { # generic mangling for other names:
953					$dbtype = lc($name);
954					}
955					$dbtype =~ s/\b(\w)/\U$1/g;
956					$dbtype =~ s/\W+/_/g;
957					}
958					# add ODBC 'behind' ADO
959					push @dbtypes, 'ODBC' if $driver eq 'ADO';
960					# add discovered dbtype in front of ADO/ODBC
961					unshift @dbtypes, $dbtype;
962					}
963					@dbtypes = &$DbTypeSubclass($dbh, \@dbtypes)
964					if (ref $DbTypeSubclass eq 'CODE');
965					$dbh->trace_msg(" DbTypeSubclass($DbTypeSubclass)=@dbtypes\n");
966					return @dbtypes;
967					}
968
969					sub _load_class {
970					my ($load_class, $missing_ok) = @_;
971					DBI->trace_msg(" _load_class($load_class, $missing_ok)\n", 2);
972					no strict 'refs';
973					return 1 if @{"$load_class\::ISA"}; # already loaded/exists
974					(my $module = $load_class) =~ s!::!/!g;
975					DBI->trace_msg(" _load_class require $module\n", 2);
976					eval { require "$module.pm"; };
977					return 1 unless $@;
978					return 0 if $missing_ok && $@ =~ /^Can't locate \Q$module.pm\E/;
979					die $@;
980					}
981
982
983					sub init_rootclass { # deprecated
984					return 1;
985					}
986
987
988					*internal = \&DBD::Switch::dr::driver;
989
990					sub driver_prefix {
991					my ($class, $driver) = @_;
992					return $dbd_class_registry{$driver}->{prefix} if exists $dbd_class_registry{$driver};
993					return;
994					}
995
996					sub available_drivers {
997					my($quiet) = @_;
998					my(@drivers, $d, $f);
999					local(*DBI::DIR, $@);
1000					my(%seen_dir, %seen_dbd);
1001					my $haveFileSpec = eval { require File::Spec };
1002					foreach $d (@INC){
1003					chomp($d); # Perl 5 beta 3 bug in #!./perl -Ilib from Test::Harness
1004					my $dbd_dir =
1005					($haveFileSpec ? File::Spec->catdir($d, 'DBD') : "$d/DBD");
1006					next unless -d $dbd_dir;
1007					next if $seen_dir{$d};
1008					$seen_dir{$d} = 1;
1009					# XXX we have a problem here with case insensitive file systems
1010					# XXX since we can't tell what case must be used when loading.
1011					opendir(DBI::DIR, $dbd_dir) \|\| Carp::carp "opendir $dbd_dir: $!\n";
1012					foreach $f (readdir(DBI::DIR)){
1013					next unless $f =~ s/\.pm$//;
1014					next if $f eq 'NullP';
1015					if ($seen_dbd{$f}){
1016					Carp::carp "DBD::$f in $d is hidden by DBD::$f in $seen_dbd{$f}\n"
1017					unless $quiet;
1018					} else {
1019					push(@drivers, $f);
1020					}
1021					$seen_dbd{$f} = $d;
1022					}
1023					closedir(DBI::DIR);
1024					}
1025
1026					# "return sort @drivers" will not DWIM in scalar context.
1027					return wantarray ? sort @drivers : @drivers;
1028					}
1029
1030					sub installed_versions {
1031					my ($class, $quiet) = @_;
1032					my %error;
1033					my %version;
1034					for my $driver ($class->available_drivers($quiet)) {
1035					next if $DBI::PurePerl && grep { -d "$_/auto/DBD/$driver" } @INC;
1036					my $drh = eval {
1037					local $SIG{__WARN__} = sub {};
1038					$class->install_driver($driver);
1039					};
1040					($error{"DBD::$driver"}=$@),next if $@;
1041					no strict 'refs';
1042					my $vers = ${"DBD::$driver" . '::VERSION'};
1043					$version{"DBD::$driver"} = $vers \|\| '?';
1044					}
1045					if (wantarray) {
1046					return map { m/^DBD::(\w+)/ ? ($1) : () } sort keys %version;
1047					}
1048					$version{"DBI"} = $DBI::VERSION;
1049					$version{"DBI::PurePerl"} = $DBI::PurePerl::VERSION if $DBI::PurePerl;
1050					if (!defined wantarray) { # void context
1051					require Config; # add more detail
1052					$version{OS} = "$^O\t($Config::Config{osvers})";
1053					$version{Perl} = "$]\t($Config::Config{archname})";
1054					$version{$_} = (($error{$_} =~ s/ \(\@INC.*//s),$error{$_})
1055					for keys %error;
1056					printf " %-16s: %s\n",$_,$version{$_}
1057					for reverse sort keys %version;
1058					}
1059					return \%version;
1060					}
1061
1062
1063					sub data_sources {
1064					my ($class, $driver, @other) = @_;
1065					my $drh = $class->install_driver($driver);
1066					my @ds = $drh->data_sources(@other);
1067					return @ds;
1068					}
1069
1070
1071					sub neat_list {
1072					my ($listref, $maxlen, $sep) = @_;
1073					$maxlen = 0 unless defined $maxlen; # 0 == use internal default
1074					$sep = ", " unless defined $sep;
1075					join($sep, map { neat($_,$maxlen) } @$listref);
1076					}
1077
1078
1079					sub dump_results { # also aliased as a method in DBD::_::st
1080					my ($sth, $maxlen, $lsep, $fsep, $fh) = @_;
1081					return 0 unless $sth;
1082					$maxlen \|\|= 35;
1083					$lsep \|\|= "\n";
1084					$fh \|\|= \*STDOUT;
1085					my $rows = 0;
1086					my $ref;
1087					while($ref = $sth->fetch) {
1088					print $fh $lsep if $rows++ and $lsep;
1089					my $str = neat_list($ref,$maxlen,$fsep);
1090					print $fh $str; # done on two lines to avoid 5.003 errors
1091					}
1092					print $fh "\n$rows rows".($DBI::err ? " ($DBI::err: $DBI::errstr)" : "")."\n";
1093					$rows;
1094					}
1095
1096
1097					sub data_diff {
1098					my ($a, $b, $logical) = @_;
1099
1100					my $diff = data_string_diff($a, $b);
1101					return "" if $logical and !$diff;
1102
1103					my $a_desc = data_string_desc($a);
1104					my $b_desc = data_string_desc($b);
1105					return "" if !$diff and $a_desc eq $b_desc;
1106
1107					$diff \|\|= "Strings contain the same sequence of characters"
1108					if length($a);
1109					$diff .= "\n" if $diff;
1110					return "a: $a_desc\nb: $b_desc\n$diff";
1111					}
1112
1113
1114					sub data_string_diff {
1115					# Compares 'logical' characters, not bytes, so a latin1 string and an
1116					# an equivalent Unicode string will compare as equal even though their
1117					# byte encodings are different.
1118					my ($a, $b) = @_;
1119					unless (defined $a and defined $b) { # one undef
1120					return ""
1121					if !defined $a and !defined $b;
1122					return "String a is undef, string b has ".length($b)." characters"
1123					if !defined $a;
1124					return "String b is undef, string a has ".length($a)." characters"
1125					if !defined $b;
1126					}
1127
1128					require utf8;
1129					# hack to cater for perl 5.6
1130					*utf8::is_utf8 = sub { (DBI::neat(shift)=~/^"/) } unless defined &utf8::is_utf8;
1131
1132					my @a_chars = (utf8::is_utf8($a)) ? unpack("U", $a) : unpack("C", $a);
1133					my @b_chars = (utf8::is_utf8($b)) ? unpack("U", $b) : unpack("C", $b);
1134					my $i = 0;
1135					while (@a_chars && @b_chars) {
1136					++$i, shift(@a_chars), shift(@b_chars), next
1137					if $a_chars[0] == $b_chars[0];# compare ordinal values
1138					my @desc = map {
1139					$_ > 255 ? # if wide character...
1140					sprintf("\\x{%04X}", $_) : # \x{...}
1141					chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
1142					sprintf("\\x%02X", $_) : # \x..
1143					chr($_) # else as themselves
1144					} ($a_chars[0], $b_chars[0]);
1145					# highlight probable double-encoding?
1146					foreach my $c ( @desc ) {
1147					next unless $c =~ m/\\x\{08(..)}/;
1148					$c .= "='" .chr(hex($1)) ."'"
1149					}
1150					return sprintf "Strings differ at index $i: a[$i]=$desc[0], b[$i]=$desc[1]";
1151					}
1152					return "String a truncated after $i characters" if @b_chars;
1153					return "String b truncated after $i characters" if @a_chars;
1154					return "";
1155					}
1156
1157
1158					sub data_string_desc { # describe a data string
1159					my ($a) = @_;
1160					require bytes;
1161					require utf8;
1162
1163					# hacks to cater for perl 5.6
1164					*utf8::is_utf8 = sub { (DBI::neat(shift)=~/^"/) } unless defined &utf8::is_utf8;
1165					*utf8::valid = sub { 1 } unless defined &utf8::valid;
1166
1167					# Give sufficient info to help diagnose at least these kinds of situations:
1168					# - valid UTF8 byte sequence but UTF8 flag not set
1169					# (might be ascii so also need to check for hibit to make it worthwhile)
1170					# - UTF8 flag set but invalid UTF8 byte sequence
1171					# could do better here, but this'll do for now
1172					my $utf8 = sprintf "UTF8 %s%s",
1173					utf8::is_utf8($a) ? "on" : "off",
1174					utf8::valid($a\|\|'') ? "" : " but INVALID encoding";
1175					return "$utf8, undef" unless defined $a;
1176					my $is_ascii = $a =~ m/^[\000-\177]*$/;
1177					return sprintf "%s, %s, %d characters %d bytes",
1178					$utf8, $is_ascii ? "ASCII" : "non-ASCII",
1179					length($a), bytes::length($a);
1180					}
1181
1182
1183					sub connect_test_perf {
1184					my($class, $dsn,$dbuser,$dbpass, $attr) = @_;
1185					Carp::croak("connect_test_perf needs hash ref as fourth arg") unless ref $attr;
1186					# these are non standard attributes just for this special method
1187					my $loops \|\|= $attr->{dbi_loops} \|\| 5;
1188					my $par \|\|= $attr->{dbi_par} \|\| 1; # parallelism
1189					my $verb \|\|= $attr->{dbi_verb} \|\| 1;
1190					my $meth \|\|= $attr->{dbi_meth} \|\| 'connect';
1191					print "$dsn: testing $loops sets of $par connections:\n";
1192					require "FileHandle.pm"; # don't let toke.c create empty FileHandle package
1193					local $\| = 1;
1194					my $drh = $class->install_driver($dsn) or Carp::croak("Can't install $dsn driver\n");
1195					# test the connection and warm up caches etc
1196					$drh->connect($dsn,$dbuser,$dbpass) or Carp::croak("connect failed: $DBI::errstr");
1197					my $t1 = dbi_time();
1198					my $loop;
1199					for $loop (1..$loops) {
1200					my @cons;
1201					print "Connecting... " if $verb;
1202					for (1..$par) {
1203					print "$_ ";
1204					push @cons, ($drh->connect($dsn,$dbuser,$dbpass)
1205					or Carp::croak("connect failed: $DBI::errstr\n"));
1206					}
1207					print "\nDisconnecting...\n" if $verb;
1208					for (@cons) {
1209					$_->disconnect or warn "disconnect failed: $DBI::errstr"
1210					}
1211					}
1212					my $t2 = dbi_time();
1213					my $td = $t2 - $t1;
1214					printf "$meth %d and disconnect them, %d times: %.4fs / %d = %.4fs\n",
1215					$par, $loops, $td, $loops$par, $td/($loops$par);
1216					return $td;
1217					}
1218
1219
1220					# Help people doing DBI->errstr, might even document it one day
1221					# XXX probably best moved to cheaper XS code if this gets documented
1222					sub err { $DBI::err }
1223					sub errstr { $DBI::errstr }
1224
1225
1226					# --- Private Internal Function for Creating New DBI Handles
1227
1228					# XXX move to PurePerl?
1229					*DBI::dr::TIEHASH = \&DBI::st::TIEHASH;
1230					*DBI::db::TIEHASH = \&DBI::st::TIEHASH;
1231
1232
1233					# These three special constructors are called by the drivers
1234					# The way they are called is likely to change.
1235
1236					our $shared_profile;
1237
1238					sub _new_drh { # called by DBD::<drivername>::driver()
1239					my ($class, $initial_attr, $imp_data) = @_;
1240					# Provide default storage for State,Err and Errstr.
1241					# Note that these are shared by all child handles by default! XXX
1242					# State must be undef to get automatic faking in DBI::var::FETCH
1243					my ($h_state_store, $h_err_store, $h_errstr_store) = (undef, undef, '');
1244					my $attr = {
1245					# these attributes get copied down to child handles by default
1246					'State' => \$h_state_store, # Holder for DBI::state
1247					'Err' => \$h_err_store, # Holder for DBI::err
1248					'Errstr' => \$h_errstr_store, # Holder for DBI::errstr
1249					'TraceLevel' => 0,
1250					FetchHashKeyName=> 'NAME',
1251					%$initial_attr,
1252					};
1253					my ($h, $i) = _new_handle('DBI::dr', '', $attr, $imp_data, $class);
1254
1255					# XXX DBI_PROFILE unless DBI::PurePerl because for some reason
1256					# it kills the t/zz_*_pp.t tests (they silently exit early)
1257					if (($ENV{DBI_PROFILE} && !$DBI::PurePerl) \|\| $shared_profile) {
1258					# The profile object created here when the first driver is loaded
1259					# is shared by all drivers so we end up with just one set of profile
1260					# data and thus the 'total time in DBI' is really the true total.
1261					if (!$shared_profile) { # first time
1262					$h->{Profile} = $ENV{DBI_PROFILE}; # write string
1263					$shared_profile = $h->{Profile}; # read and record object
1264					}
1265					else {
1266					$h->{Profile} = $shared_profile;
1267					}
1268					}
1269					return $h unless wantarray;
1270					($h, $i);
1271					}
1272
1273					sub _new_dbh { # called by DBD::<drivername>::dr::connect()
1274					my ($drh, $attr, $imp_data) = @_;
1275					my $imp_class = $drh->{ImplementorClass}
1276					or Carp::croak("DBI _new_dbh: $drh has no ImplementorClass");
1277					substr($imp_class,-4,4) = '::db';
1278					my $app_class = ref $drh;
1279					substr($app_class,-4,4) = '::db';
1280					$attr->{Err} \|\|= \my $err;
1281					$attr->{Errstr} \|\|= \my $errstr;
1282					$attr->{State} \|\|= \my $state;
1283					_new_handle($app_class, $drh, $attr, $imp_data, $imp_class);
1284					}
1285
1286					sub _new_sth { # called by DBD::<drivername>::db::prepare)
1287					my ($dbh, $attr, $imp_data) = @_;
1288					my $imp_class = $dbh->{ImplementorClass}
1289					or Carp::croak("DBI _new_sth: $dbh has no ImplementorClass");
1290					substr($imp_class,-4,4) = '::st';
1291					my $app_class = ref $dbh;
1292					substr($app_class,-4,4) = '::st';
1293					_new_handle($app_class, $dbh, $attr, $imp_data, $imp_class);
1294					}
1295
1296
1297					# end of DBI package
1298
- -
1301					# --------------------------------------------------------------------
1302					# === The internal DBI Switch pseudo 'driver' class ===
1303
1304					{ package # hide from PAUSE
1305					DBD::Switch::dr;
1306					DBI->setup_driver('DBD::Switch'); # sets up @ISA
1307
1308					$DBD::Switch::dr::imp_data_size = 0;
1309					$DBD::Switch::dr::imp_data_size = 0; # avoid typo warning
1310					my $drh;
1311
1312					sub driver {
1313					return $drh if $drh; # a package global
1314
1315					my $inner;
1316					($drh, $inner) = DBI::_new_drh('DBD::Switch::dr', {
1317					'Name' => 'Switch',
1318					'Version' => $DBI::VERSION,
1319					'Attribution' => "DBI $DBI::VERSION by Tim Bunce",
1320					});
1321					Carp::croak("DBD::Switch init failed!") unless ($drh && $inner);
1322					return $drh;
1323					}
1324					sub CLONE {
1325					undef $drh;
1326					}
1327
1328					sub FETCH {
1329					my($drh, $key) = @_;
1330					return DBI->trace if $key eq 'DebugDispatch';
1331					return undef if $key eq 'DebugLog'; # not worth fetching, sorry
1332					return $drh->DBD::_::dr::FETCH($key);
1333					undef;
1334					}
1335					sub STORE {
1336					my($drh, $key, $value) = @_;
1337					if ($key eq 'DebugDispatch') {
1338					DBI->trace($value);
1339					} elsif ($key eq 'DebugLog') {
1340					DBI->trace(-1, $value);
1341					} else {
1342					$drh->DBD::_::dr::STORE($key, $value);
1343					}
1344					}
1345					}
1346
1347
1348					# --------------------------------------------------------------------
1349					# === OPTIONAL MINIMAL BASE CLASSES FOR DBI SUBCLASSES ===
1350
1351					# We only define default methods for harmless functions.
1352					# We don't, for example, define a DBD::_::st::prepare()
1353
1354					{ package # hide from PAUSE
1355					DBD::_::common; # ====== Common base class methods ======
1356					use strict;
1357
1358					# methods common to all handle types:
1359
1360					# generic TIEHASH default methods:
1361					sub FIRSTKEY { }
1362					sub NEXTKEY { }
1363					sub EXISTS { defined($_[0]->FETCH($_[1])) } # XXX undef?
1364					sub CLEAR { Carp::carp "Can't CLEAR $_[0] (DBI)" }
1365
1366					sub FETCH_many { # XXX should move to C one day
1367					my $h = shift;
1368					# scalar is needed to workaround drivers that return an empty list
1369					# for some attributes
1370					return map { scalar $h->FETCH($_) } @_;
1371					}
1372
1373					*dump_handle = \&DBI::dump_handle;
1374
1375					sub install_method {
1376					# special class method called directly by apps and/or drivers
1377					# to install new methods into the DBI dispatcher
1378					# DBD::Foo::db->install_method("foo_mumble", { usage => [...], options => '...' });
1379					my ($class, $method, $attr) = @_;
1380					Carp::croak("Class '$class' must begin with DBD:: and end with ::db or ::st")
1381					unless $class =~ /^DBD::(\w+)::(dr\|db\|st)$/;
1382					my ($driver, $subtype) = ($1, $2);
1383					Carp::croak("invalid method name '$method'")
1384					unless $method =~ m/^([a-z]+_)\w+$/;
1385					my $prefix = $1;
1386					my $reg_info = $dbd_prefix_registry->{$prefix};
1387					Carp::carp("method name prefix '$prefix' is not associated with a registered driver") unless $reg_info;
1388
1389					my $full_method = "DBI::${subtype}::$method";
1390					$DBI::installed_methods{$full_method} = $attr;
1391
1392					my (undef, $filename, $line) = caller;
1393					# XXX reformat $attr as needed for _install_method
1394					my %attr = %{$attr\|\|{}}; # copy so we can edit
1395					DBI->_install_method("DBI::${subtype}::$method", "$filename at line $line", \%attr);
1396					}
1397
1398					sub parse_trace_flags {
1399					my ($h, $spec) = @_;
1400					my $level = 0;
1401					my $flags = 0;
1402					my @unknown;
1403					for my $word (split /\s[\|&,]\s/, $spec) {
1404					if (DBI::looks_like_number($word) && $word <= 0xF && $word >= 0) {
1405					$level = $word;
1406					} elsif ($word eq 'ALL') {
1407					$flags = 0x7FFFFFFF; # XXX last bit causes negative headaches
1408					last;
1409					} elsif (my $flag = $h->parse_trace_flag($word)) {
1410					$flags \|= $flag;
1411					}
1412					else {
1413					push @unknown, $word;
1414					}
1415					}
1416					if (@unknown && (ref $h ? $h->FETCH('Warn') : 1)) {
1417					Carp::carp("$h->parse_trace_flags($spec) ignored unknown trace flags: ".
1418					join(" ", map { DBI::neat($_) } @unknown));
1419					}
1420					$flags \|= $level;
1421					return $flags;
1422					}
1423
1424					sub parse_trace_flag {
1425					my ($h, $name) = @_;
1426					# 0xddDDDDrL (driver, DBI, reserved, Level)
1427					return 0x00000100 if $name eq 'SQL';
1428					return 0x00000200 if $name eq 'CON';
1429					return 0x00000400 if $name eq 'ENC';
1430					return 0x00000800 if $name eq 'DBD';
1431					return 0x00001000 if $name eq 'TXN';
1432					return;
1433					}
1434
1435					sub private_attribute_info {
1436					return undef;
1437					}
1438
1439					sub visit_child_handles {
1440					my ($h, $code, $info) = @_;
1441					$info = {} if not defined $info;
1442					for my $ch (@{ $h->{ChildHandles} \|\| []}) {
1443					next unless $ch;
1444					my $child_info = $code->($ch, $info)
1445					or next;
1446					$ch->visit_child_handles($code, $child_info);
1447					}
1448					return $info;
1449					}
1450					}
1451
1452
1453					{ package # hide from PAUSE
1454					DBD::_::dr; # ====== DRIVER ======
1455					@DBD::_::dr::ISA = qw(DBD::_::common);
1456					use strict;
1457
1458					sub default_user {
1459					my ($drh, $user, $pass, $attr) = @_;
1460					$user = $ENV{DBI_USER} unless defined $user;
1461					$pass = $ENV{DBI_PASS} unless defined $pass;
1462					return ($user, $pass);
1463					}
1464
1465					sub connect { # normally overridden, but a handy default
1466					my ($drh, $dsn, $user, $auth) = @_;
1467					my ($this) = DBI::_new_dbh($drh, {
1468					'Name' => $dsn,
1469					});
1470					# XXX debatable as there's no "server side" here
1471					# (and now many uses would trigger warnings on DESTROY)
1472					# $this->STORE(Active => 1);
1473					# so drivers should set it in their own connect
1474					$this;
1475					}
1476
1477
1478					sub connect_cached {
1479					my $drh = shift;
1480					my ($dsn, $user, $auth, $attr) = @_;
1481
1482					my $cache = $drh->{CachedKids} \|\|= {};
1483					my $key = do { local $^W;
1484					join "!\001", $dsn, $user, $auth, DBI::_concat_hash_sorted($attr, "=\001", ",\001", 0, 0)
1485					};
1486					my $dbh = $cache->{$key};
1487					$drh->trace_msg(sprintf(" connect_cached: key '$key', cached dbh $dbh\n", DBI::neat($key), DBI::neat($dbh)))
1488					if (($DBI::dbi_debug & 0xF) >= 4);
1489
1490					my $cb = $attr->{Callbacks}; # take care not to autovivify
1491					if ($dbh && $dbh->FETCH('Active') && eval { $dbh->ping }) {
1492					# If the caller has provided a callback then call it
1493					if ($cb and $cb = $cb->{"connect_cached.reused"}) {
1494					local $_ = "connect_cached.reused";
1495					$cb->($dbh, $dsn, $user, $auth, $attr);
1496					}
1497					return $dbh;
1498					}
1499
1500					# If the caller has provided a callback then call it
1501					if ($cb and (my $new_cb = $cb->{"connect_cached.new"})) {
1502					local $_ = "connect_cached.new";
1503					$new_cb->($dbh, $dsn, $user, $auth, $attr); # $dbh is dead or undef
1504					}
1505
1506					$dbh = $drh->connect(@_);
1507					$cache->{$key} = $dbh; # replace prev entry, even if connect failed
1508					if ($cb and (my $conn_cb = $cb->{"connect_cached.connected"})) {
1509					local $_ = "connect_cached.connected";
1510					$conn_cb->($dbh, $dsn, $user, $auth, $attr);
1511					}
1512					return $dbh;
1513					}
1514
1515					}
1516
1517
1518					{ package # hide from PAUSE
1519					DBD::_::db; # ====== DATABASE ======
1520					@DBD::_::db::ISA = qw(DBD::_::common);
1521					use strict;
1522
1523					sub clone {
1524					my ($old_dbh, $attr) = @_;
1525
1526					my $closure = $old_dbh->{dbi_connect_closure}
1527					or return $old_dbh->set_err($DBI::stderr, "Can't clone handle");
1528
1529					unless ($attr) { # XXX deprecated, caller should always pass a hash ref
1530					# copy attributes visible in the attribute cache
1531					keys %$old_dbh; # reset iterator
1532					while ( my ($k, $v) = each %$old_dbh ) {
1533					# ignore non-code refs, i.e., caches, handles, Err etc
1534					next if ref $v && ref $v ne 'CODE'; # HandleError etc
1535					$attr->{$k} = $v;
1536					}
1537					# explicitly set attributes which are unlikely to be in the
1538					# attribute cache, i.e., boolean's and some others
1539					$attr->{$_} = $old_dbh->FETCH($_) for (qw(
1540					AutoCommit ChopBlanks InactiveDestroy AutoInactiveDestroy
1541					LongTruncOk PrintError PrintWarn Profile RaiseError
1542					ShowErrorStatement TaintIn TaintOut
1543					));
1544					}
1545
1546					# use Data::Dumper; warn Dumper([$old_dbh, $attr]);
1547					my $new_dbh = &$closure($old_dbh, $attr);
1548					unless ($new_dbh) {
1549					# need to copy err/errstr from driver back into $old_dbh
1550					my $drh = $old_dbh->{Driver};
1551					return $old_dbh->set_err($drh->err, $drh->errstr, $drh->state);
1552					}
1553					$new_dbh->{dbi_connect_closure} = $closure;
1554					return $new_dbh;
1555					}
1556
1557					sub quote_identifier {
1558					my ($dbh, @id) = @_;
1559					my $attr = (@id > 3 && ref($id[-1])) ? pop @id : undef;
1560
1561					my $info = $dbh->{dbi_quote_identifier_cache} \|\|= [
1562					$dbh->get_info(29) \|\| '"', # SQL_IDENTIFIER_QUOTE_CHAR
1563					$dbh->get_info(41) \|\| '.', # SQL_CATALOG_NAME_SEPARATOR
1564					$dbh->get_info(114) \|\| 1, # SQL_CATALOG_LOCATION
1565					];
1566
1567					my $quote = $info->[0];
1568					foreach (@id) { # quote the elements
1569					next unless defined;
1570					s/$quote/$quote$quote/g; # escape embedded quotes
1571					$_ = qq{$quote$_$quote};
1572					}
1573
1574					# strip out catalog if present for special handling
1575					my $catalog = (@id >= 3) ? shift @id : undef;
1576
1577					# join the dots, ignoring any null/undef elements (ie schema)
1578					my $quoted_id = join '.', grep { defined } @id;
1579
1580					if ($catalog) { # add catalog correctly
1581					$quoted_id = ($info->[2] == 2) # SQL_CL_END
1582					? $quoted_id . $info->[1] . $catalog
1583					: $catalog . $info->[1] . $quoted_id;
1584					}
1585					return $quoted_id;
1586					}
1587
1588					sub quote {
1589					my ($dbh, $str, $data_type) = @_;
1590
1591					return "NULL" unless defined $str;
1592					unless ($data_type) {
1593					$str =~ s/'/''/g; # ISO SQL2
1594					return "'$str'";
1595					}
1596
1597					my $dbi_literal_quote_cache = $dbh->{'dbi_literal_quote_cache'} \|\|= [ {} , {} ];
1598					my ($prefixes, $suffixes) = @$dbi_literal_quote_cache;
1599
1600					my $lp = $prefixes->{$data_type};
1601					my $ls = $suffixes->{$data_type};
1602
1603					if ( ! defined $lp \|\| ! defined $ls ) {
1604					my $ti = $dbh->type_info($data_type);
1605					$lp = $prefixes->{$data_type} = $ti ? $ti->{LITERAL_PREFIX} \|\| "" : "'";
1606					$ls = $suffixes->{$data_type} = $ti ? $ti->{LITERAL_SUFFIX} \|\| "" : "'";
1607					}
1608					return $str unless $lp \|\| $ls; # no quoting required
1609
1610					# XXX don't know what the standard says about escaping
1611					# in the 'general case' (where $lp != "'").
1612					# So we just do this and hope:
1613					$str =~ s/$lp/$lp$lp/g
1614					if $lp && $lp eq $ls && ($lp eq "'" \|\| $lp eq '"');
1615					return "$lp$str$ls";
1616					}
1617
1618					sub rows { -1 } # here so $DBI::rows 'works' after using $dbh
1619
1620					sub do {
1621					my($dbh, $statement, $attr, @params) = @_;
1622					my $sth = $dbh->prepare($statement, $attr) or return undef;
1623					$sth->execute(@params) or return undef;
1624					my $rows = $sth->rows;
1625					($rows == 0) ? "0E0" : $rows;
1626					}
1627
1628					sub _do_selectrow {
1629					my ($method, $dbh, $stmt, $attr, @bind) = @_;
1630					my $sth = ((ref $stmt) ? $stmt : $dbh->prepare($stmt, $attr))
1631					or return;
1632					$sth->execute(@bind)
1633					or return;
1634					my $row = $sth->$method()
1635					and $sth->finish;
1636					return $row;
1637					}
1638
1639					sub selectrow_hashref { return _do_selectrow('fetchrow_hashref', @_); }
1640
1641					# XXX selectrow_array/ref also have C implementations in Driver.xst
1642					sub selectrow_arrayref { return _do_selectrow('fetchrow_arrayref', @_); }
1643					sub selectrow_array {
1644					my $row = _do_selectrow('fetchrow_arrayref', @_) or return;
1645					return $row->[0] unless wantarray;
1646					return @$row;
1647					}
1648
1649					# XXX selectall_arrayref also has C implementation in Driver.xst
1650					# which fallsback to this if a slice is given
1651					sub selectall_arrayref {
1652					my ($dbh, $stmt, $attr, @bind) = @_;
1653					my $sth = (ref $stmt) ? $stmt : $dbh->prepare($stmt, $attr)
1654					or return;
1655					$sth->execute(@bind) \|\| return;
1656					my $slice = $attr->{Slice}; # typically undef, else hash or array ref
1657					if (!$slice and $slice=$attr->{Columns}) {
1658					if (ref $slice eq 'ARRAY') { # map col idx to perl array idx
1659					$slice = [ @{$attr->{Columns}} ]; # take a copy
1660					for (@$slice) { $_-- }
1661					}
1662					}
1663					my $rows = $sth->fetchall_arrayref($slice, my $MaxRows = $attr->{MaxRows});
1664					$sth->finish if defined $MaxRows;
1665					return $rows;
1666					}
1667
1668					sub selectall_hashref {
1669					my ($dbh, $stmt, $key_field, $attr, @bind) = @_;
1670					my $sth = (ref $stmt) ? $stmt : $dbh->prepare($stmt, $attr);
1671					return unless $sth;
1672					$sth->execute(@bind) \|\| return;
1673					return $sth->fetchall_hashref($key_field);
1674					}
1675
1676					sub selectcol_arrayref {
1677					my ($dbh, $stmt, $attr, @bind) = @_;
1678					my $sth = (ref $stmt) ? $stmt : $dbh->prepare($stmt, $attr);
1679					return unless $sth;
1680					$sth->execute(@bind) \|\| return;
1681					my @columns = ($attr->{Columns}) ? @{$attr->{Columns}} : (1);
1682					my @values = (undef) x @columns;
1683					my $idx = 0;
1684					for (@columns) {
1685					$sth->bind_col($_, \$values[$idx++]) \|\| return;
1686					}
1687					my @col;
1688					if (my $max = $attr->{MaxRows}) {
1689					push @col, @values while 0 < $max-- && $sth->fetch;
1690					}
1691					else {
1692					push @col, @values while $sth->fetch;
1693					}
1694					return \@col;
1695					}
1696
1697					sub prepare_cached {
1698					my ($dbh, $statement, $attr, $if_active) = @_;
1699
1700					# Needs support at dbh level to clear cache before complaining about
1701					# active children. The XS template code does this. Drivers not using
1702					# the template must handle clearing the cache themselves.
1703					my $cache = $dbh->{CachedKids} \|\|= {};
1704					my $key = do { local $^W;
1705					join "!\001", $statement, DBI::_concat_hash_sorted($attr, "=\001", ",\001", 0, 0)
1706					};
1707					my $sth = $cache->{$key};
1708
1709					if ($sth) {
1710					return $sth unless $sth->FETCH('Active');
1711					Carp::carp("prepare_cached($statement) statement handle $sth still Active")
1712					unless ($if_active \|\|= 0);
1713					$sth->finish if $if_active <= 1;
1714					return $sth if $if_active <= 2;
1715					}
1716
1717	1	16µs	1	65µs	$sth = $dbh->prepare($statement, $attr); # spent 65µs making 1 call to DBD::mysql::db::prepare
1718					$cache->{$key} = $sth if $sth;
1719
1720					return $sth;
1721					}
1722
1723					sub ping {
1724					my $dbh = shift;
1725					# "0 but true" is a special kind of true 0 that is used here so
1726					# applications can check if the ping was a real ping or not
1727					($dbh->FETCH('Active')) ? "0 but true" : 0;
1728					}
1729
1730					sub begin_work {
1731					my $dbh = shift;
1732					return $dbh->set_err($DBI::stderr, "Already in a transaction")
1733					unless $dbh->FETCH('AutoCommit');
1734					$dbh->STORE('AutoCommit', 0); # will croak if driver doesn't support it
1735					$dbh->STORE('BegunWork', 1); # trigger post commit/rollback action
1736					return 1;
1737					}
1738
1739					sub primary_key {
1740					my ($dbh, @args) = @_;
1741					my $sth = $dbh->primary_key_info(@args) or return;
1742					my ($row, @col);
1743					push @col, $row->[3] while ($row = $sth->fetch);
1744					Carp::croak("primary_key method not called in list context")
1745					unless wantarray; # leave us some elbow room
1746					return @col;
1747					}
1748
1749					sub tables {
1750					my ($dbh, @args) = @_;
1751					my $sth = $dbh->table_info(@args[0,1,2,3,4]) or return;
1752					my $tables = $sth->fetchall_arrayref or return;
1753					my @tables;
1754					if ($dbh->get_info(29)) { # SQL_IDENTIFIER_QUOTE_CHAR
1755					@tables = map { $dbh->quote_identifier( @{$_}[0,1,2] ) } @$tables;
1756					}
1757					else { # temporary old style hack (yeach)
1758					@tables = map {
1759					my $name = $_->[2];
1760					if ($_->[1]) {
1761					my $schema = $_->[1];
1762					# a sad hack (mostly for Informix I recall)
1763					my $quote = ($schema eq uc($schema)) ? '' : '"';
1764					$name = "$quote$schema$quote.$name"
1765					}
1766					$name;
1767					} @$tables;
1768					}
1769					return @tables;
1770					}
1771
1772					sub type_info { # this should be sufficient for all drivers
1773					my ($dbh, $data_type) = @_;
1774					my $idx_hash;
1775					my $tia = $dbh->{dbi_type_info_row_cache};
1776					if ($tia) {
1777					$idx_hash = $dbh->{dbi_type_info_idx_cache};
1778					}
1779					else {
1780					my $temp = $dbh->type_info_all;
1781					return unless $temp && @$temp;
1782					# we cache here because type_info_all may be expensive to call
1783					# (and we take a copy so the following shift can't corrupt
1784					# the data that may be returned by future calls to type_info_all)
1785					$tia = $dbh->{dbi_type_info_row_cache} = [ @$temp ];
1786					$idx_hash = $dbh->{dbi_type_info_idx_cache} = shift @$tia;
1787					}
1788
1789					my $dt_idx = $idx_hash->{DATA_TYPE} \|\| $idx_hash->{data_type};
1790					Carp::croak("type_info_all returned non-standard DATA_TYPE index value ($dt_idx != 1)")
1791					if $dt_idx && $dt_idx != 1;
1792
1793					# --- simple DATA_TYPE match filter
1794					my @ti;
1795					my @data_type_list = (ref $data_type) ? @$data_type : ($data_type);
1796					foreach $data_type (@data_type_list) {
1797					if (defined($data_type) && $data_type != DBI::SQL_ALL_TYPES()) {
1798					push @ti, grep { $_->[$dt_idx] == $data_type } @$tia;
1799					}
1800					else { # SQL_ALL_TYPES
1801					push @ti, @$tia;
1802					}
1803					last if @ti; # found at least one match
1804					}
1805
1806					# --- format results into list of hash refs
1807					my $idx_fields = keys %$idx_hash;
1808					my @idx_names = map { uc($_) } keys %$idx_hash;
1809					my @idx_values = values %$idx_hash;
1810					Carp::croak "type_info_all result has $idx_fields keys but ".(@{$ti[0]})." fields"
1811					if @ti && @{$ti[0]} != $idx_fields;
1812					my @out = map {
1813					my %h; @h{@idx_names} = @{$_}[ @idx_values ]; \%h;
1814					} @ti;
1815					return $out[0] unless wantarray;
1816					return @out;
1817					}
1818
1819					sub data_sources {
1820					my ($dbh, @other) = @_;
1821					my $drh = $dbh->{Driver}; # XXX proxy issues?
1822					return $drh->data_sources(@other);
1823					}
1824
1825					}
1826
1827
1828					{ package # hide from PAUSE
1829					DBD::_::st; # ====== STATEMENT ======
1830					@DBD::_::st::ISA = qw(DBD::_::common);
1831					use strict;
1832
1833					sub bind_param { Carp::croak("Can't bind_param, not implement by driver") }
1834
1835					#
1836					# ********************************************************
1837					#
1838					# BEGIN ARRAY BINDING
1839					#
1840					# Array binding support for drivers which don't support
1841					# array binding, but have sufficient interfaces to fake it.
1842					# NOTE: mixing scalars and arrayrefs requires using bind_param_array
1843					# for all params...unless we modify bind_param for the default
1844					# case...
1845					#
1846					# 2002-Apr-10 D. Arnold
1847
1848					sub bind_param_array {
1849					my $sth = shift;
1850					my ($p_id, $value_array, $attr) = @_;
1851
1852					return $sth->set_err($DBI::stderr, "Value for parameter $p_id must be a scalar or an arrayref, not a ".ref($value_array))
1853					if defined $value_array and ref $value_array and ref $value_array ne 'ARRAY';
1854
1855					return $sth->set_err($DBI::stderr, "Can't use named placeholder '$p_id' for non-driver supported bind_param_array")
1856					unless DBI::looks_like_number($p_id); # because we rely on execute(@ary) here
1857
1858					return $sth->set_err($DBI::stderr, "Placeholder '$p_id' is out of range")
1859					if $p_id <= 0; # can't easily/reliably test for too big
1860
1861					# get/create arrayref to hold params
1862					my $hash_of_arrays = $sth->{ParamArrays} \|\|= { };
1863
1864					# If the bind has attribs then we rely on the driver conforming to
1865					# the DBI spec in that a single bind_param() call with those attribs
1866					# makes them 'sticky' and apply to all later execute(@values) calls.
1867					# Since we only call bind_param() if we're given attribs then
1868					# applications using drivers that don't support bind_param can still
1869					# use bind_param_array() so long as they don't pass any attribs.
1870
1871					$$hash_of_arrays{$p_id} = $value_array;
1872					return $sth->bind_param($p_id, undef, $attr)
1873					if $attr;
1874					1;
1875					}
1876
1877					sub bind_param_inout_array {
1878					my $sth = shift;
1879					# XXX not supported so we just call bind_param_array instead
1880					# and then return an error
1881					my ($p_num, $value_array, $attr) = @_;
1882					$sth->bind_param_array($p_num, $value_array, $attr);
1883					return $sth->set_err($DBI::stderr, "bind_param_inout_array not supported");
1884					}
1885
1886					sub bind_columns {
1887					my $sth = shift;
1888					my $fields = $sth->FETCH('NUM_OF_FIELDS') \|\| 0;
1889					if ($fields <= 0 && !$sth->{Active}) {
1890					return $sth->set_err($DBI::stderr, "Statement has no result columns to bind"
1891					." (perhaps you need to successfully call execute first)");
1892					}
1893					# Backwards compatibility for old-style call with attribute hash
1894					# ref as first arg. Skip arg if undef or a hash ref.
1895					my $attr;
1896					$attr = shift if !defined $_[0] or ref($_[0]) eq 'HASH';
1897
1898					my $idx = 0;
1899					$sth->bind_col(++$idx, shift, $attr) or return
1900					while (@_ and $idx < $fields);
1901
1902					return $sth->set_err($DBI::stderr, "bind_columns called with ".($idx+@_)." values but $fields are needed")
1903					if @_ or $idx != $fields;
1904
1905					return 1;
1906					}
1907
1908					sub execute_array {
1909					my $sth = shift;
1910					my ($attr, @array_of_arrays) = @_;
1911					my $NUM_OF_PARAMS = $sth->FETCH('NUM_OF_PARAMS'); # may be undef at this point
1912
1913					# get tuple status array or hash attribute
1914					my $tuple_sts = $attr->{ArrayTupleStatus};
1915					return $sth->set_err($DBI::stderr, "ArrayTupleStatus attribute must be an arrayref")
1916					if $tuple_sts and ref $tuple_sts ne 'ARRAY';
1917
1918					# bind all supplied arrays
1919					if (@array_of_arrays) {
1920					$sth->{ParamArrays} = { }; # clear out old params
1921					return $sth->set_err($DBI::stderr,
1922					@array_of_arrays." bind values supplied but $NUM_OF_PARAMS expected")
1923					if defined ($NUM_OF_PARAMS) && @array_of_arrays != $NUM_OF_PARAMS;
1924					$sth->bind_param_array($_, $array_of_arrays[$_-1]) or return
1925					foreach (1..@array_of_arrays);
1926					}
1927
1928					my $fetch_tuple_sub;
1929
1930					if ($fetch_tuple_sub = $attr->{ArrayTupleFetch}) { # fetch on demand
1931
1932					return $sth->set_err($DBI::stderr,
1933					"Can't use both ArrayTupleFetch and explicit bind values")
1934					if @array_of_arrays; # previous bind_param_array calls will simply be ignored
1935
1936					if (UNIVERSAL::isa($fetch_tuple_sub,'DBI::st')) {
1937					my $fetch_sth = $fetch_tuple_sub;
1938					return $sth->set_err($DBI::stderr,
1939					"ArrayTupleFetch sth is not Active, need to execute() it first")
1940					unless $fetch_sth->{Active};
1941					# check column count match to give more friendly message
1942					my $NUM_OF_FIELDS = $fetch_sth->{NUM_OF_FIELDS};
1943					return $sth->set_err($DBI::stderr,
1944					"$NUM_OF_FIELDS columns from ArrayTupleFetch sth but $NUM_OF_PARAMS expected")
1945					if defined($NUM_OF_FIELDS) && defined($NUM_OF_PARAMS)
1946					&& $NUM_OF_FIELDS != $NUM_OF_PARAMS;
1947					$fetch_tuple_sub = sub { $fetch_sth->fetchrow_arrayref };
1948					}
1949					elsif (!UNIVERSAL::isa($fetch_tuple_sub,'CODE')) {
1950					return $sth->set_err($DBI::stderr, "ArrayTupleFetch '$fetch_tuple_sub' is not a code ref or statement handle");
1951					}
1952
1953					}
1954					else {
1955					my $NUM_OF_PARAMS_given = keys %{ $sth->{ParamArrays} \|\| {} };
1956					return $sth->set_err($DBI::stderr,
1957					"$NUM_OF_PARAMS_given bind values supplied but $NUM_OF_PARAMS expected")
1958					if defined($NUM_OF_PARAMS) && $NUM_OF_PARAMS != $NUM_OF_PARAMS_given;
1959
1960					# get the length of a bound array
1961					my $maxlen;
1962					my %hash_of_arrays = %{$sth->{ParamArrays}};
1963					foreach (keys(%hash_of_arrays)) {
1964					my $ary = $hash_of_arrays{$_};
1965					next unless ref $ary eq 'ARRAY';
1966					$maxlen = @$ary if !$maxlen \|\| @$ary > $maxlen;
1967					}
1968					# if there are no arrays then execute scalars once
1969					$maxlen = 1 unless defined $maxlen;
1970					my @bind_ids = 1..keys(%hash_of_arrays);
1971
1972					my $tuple_idx = 0;
1973					$fetch_tuple_sub = sub {
1974					return if $tuple_idx >= $maxlen;
1975					my @tuple = map {
1976					my $a = $hash_of_arrays{$_};
1977					ref($a) ? $a->[$tuple_idx] : $a
1978					} @bind_ids;
1979					++$tuple_idx;
1980					return \@tuple;
1981					};
1982					}
1983					# pass thru the callers scalar or list context
1984					return $sth->execute_for_fetch($fetch_tuple_sub, $tuple_sts);
1985					}
1986
1987					sub execute_for_fetch {
1988					my ($sth, $fetch_tuple_sub, $tuple_status) = @_;
1989					# start with empty status array
1990					($tuple_status) ? @$tuple_status = () : $tuple_status = [];
1991
1992					my $rc_total = 0;
1993					my $err_count;
1994					while ( my $tuple = &$fetch_tuple_sub() ) {
1995					if ( my $rc = $sth->execute(@$tuple) ) {
1996					push @$tuple_status, $rc;
1997					$rc_total = ($rc >= 0 && $rc_total >= 0) ? $rc_total + $rc : -1;
1998					}
1999					else {
2000					$err_count++;
2001					push @$tuple_status, [ $sth->err, $sth->errstr, $sth->state ];
2002					# XXX drivers implementing execute_for_fetch could opt to "last;" here
2003					# if they know the error code means no further executes will work.
2004					}
2005					}
2006					my $tuples = @$tuple_status;
2007					return $sth->set_err($DBI::stderr, "executing $tuples generated $err_count errors")
2008					if $err_count;
2009					$tuples \|\|= "0E0";
2010					return $tuples unless wantarray;
2011					return ($tuples, $rc_total);
2012					}
2013
2014
2015					sub fetchall_arrayref { # ALSO IN Driver.xst
2016					my ($sth, $slice, $max_rows) = @_;
2017
2018					# when batch fetching with $max_rows were very likely to try to
2019					# fetch the 'next batch' after the previous batch returned
2020					# <=$max_rows. So don't treat that as an error.
2021					return undef if $max_rows and not $sth->FETCH('Active');
2022
2023					my $mode = ref($slice) \|\| 'ARRAY';
2024					my @rows;
2025
2026					if ($mode eq 'ARRAY') {
2027					my $row;
2028					# we copy the array here because fetch (currently) always
2029					# returns the same array ref. XXX
2030					if ($slice && @$slice) {
2031					$max_rows = -1 unless defined $max_rows;
2032					push @rows, [ @{$row}[ @$slice] ]
2033					while($max_rows-- and $row = $sth->fetch);
2034					}
2035					elsif (defined $max_rows) {
2036					push @rows, [ @$row ]
2037					while($max_rows-- and $row = $sth->fetch);
2038					}
2039					else {
2040					push @rows, [ @$row ] while($row = $sth->fetch);
2041					}
2042					return \@rows
2043					}
2044
2045					my %row;
2046					if ($mode eq 'REF' && ref($$slice) eq 'HASH') { # \{ $idx => $name }
2047					keys %$$slice; # reset the iterator
2048					while ( my ($idx, $name) = each %$$slice ) {
2049					$sth->bind_col($idx+1, \$row{$name});
2050					}
2051					}
2052					elsif ($mode eq 'HASH') {
2053					if (keys %$slice) {
2054					keys %$slice; # reset the iterator
2055					my $name2idx = $sth->FETCH('NAME_lc_hash');
2056					while ( my ($name, $unused) = each %$slice ) {
2057					my $idx = $name2idx->{lc $name};
2058					return $sth->set_err($DBI::stderr, "Invalid column name '$name' for slice")
2059					if not defined $idx;
2060					$sth->bind_col($idx+1, \$row{$name});
2061					}
2062					}
2063					else {
2064					$sth->bind_columns( \( @row{ @{$sth->FETCH($sth->FETCH('FetchHashKeyName')) } } ) );
2065					}
2066					}
2067					else {
2068					return $sth->set_err($DBI::stderr, "fetchall_arrayref($mode) invalid");
2069					}
2070
2071					if (not defined $max_rows) {
2072					push @rows, { %row } while ($sth->fetch); # full speed ahead!
2073					}
2074					else {
2075					push @rows, { %row } while ($max_rows-- and $sth->fetch);
2076					}
2077
2078					return \@rows;
2079					}
2080
2081					sub fetchall_hashref {
2082					my ($sth, $key_field) = @_;
2083
2084					my $hash_key_name = $sth->{FetchHashKeyName} \|\| 'NAME';
2085					my $names_hash = $sth->FETCH("${hash_key_name}_hash");
2086					my @key_fields = (ref $key_field) ? @$key_field : ($key_field);
2087					my @key_indexes;
2088					my $num_of_fields = $sth->FETCH('NUM_OF_FIELDS');
2089					foreach (@key_fields) {
2090					my $index = $names_hash->{$_}; # perl index not column
2091					$index = $_ - 1 if !defined $index && DBI::looks_like_number($_) && $_>=1 && $_ <= $num_of_fields;
2092					return $sth->set_err($DBI::stderr, "Field '$_' does not exist (not one of @{[keys %$names_hash]})")
2093					unless defined $index;
2094					push @key_indexes, $index;
2095					}
2096					my $rows = {};
2097					my $NAME = $sth->FETCH($hash_key_name);
2098					my @row = (undef) x $num_of_fields;
2099					$sth->bind_columns(\(@row));
2100					while ($sth->fetch) {
2101					my $ref = $rows;
2102					$ref = $ref->{$row[$_]} \|\|= {} for @key_indexes;
2103					@{$ref}{@$NAME} = @row;
2104					}
2105					return $rows;
2106					}
2107
2108					*dump_results = \&DBI::dump_results;
2109
2110					sub blob_copy_to_file { # returns length or undef on error
2111					my($self, $field, $filename_or_handleref, $blocksize) = @_;
2112					my $fh = $filename_or_handleref;
2113					my($len, $buf) = (0, "");
2114					$blocksize \|\|= 512; # not too ambitious
2115					local(*FH);
2116					unless(ref $fh) {
2117					open(FH, ">$fh") \|\| return undef;
2118					$fh = \*FH;
2119					}
2120					while(defined($self->blob_read($field, $len, $blocksize, \$buf))) {
2121					print $fh $buf;
2122					$len += length $buf;
2123					}
2124					close(FH);
2125					$len;
2126					}
2127
2128					sub more_results {
2129					shift->{syb_more_results}; # handy grandfathering
2130					}
2131
2132					}
2133
2134					unless ($DBI::PurePerl) { # See install_driver
2135					{ @DBD::_mem::dr::ISA = qw(DBD::_mem::common); }
2136					{ @DBD::_mem::db::ISA = qw(DBD::_mem::common); }
2137					{ @DBD::_mem::st::ISA = qw(DBD::_mem::common); }
2138					# DBD::_mem::common::DESTROY is implemented in DBI.xs
2139					}
2140
2141					1;
2142					__END__
2143
2144					=head1 DESCRIPTION
2145
2146					The DBI is a database access module for the Perl programming language. It defines
2147					a set of methods, variables, and conventions that provide a consistent
2148					database interface, independent of the actual database being used.
2149
2150					It is important to remember that the DBI is just an interface.
2151					The DBI is a layer
2152					of "glue" between an application and one or more database I<driver>
2153					modules. It is the driver modules which do most of the real work. The DBI
2154					provides a standard interface and framework for the drivers to operate
2155					within.
2156
2157					This document often uses terms like I<references>, I<objects>,
2158					I<methods>. If you're not familiar with those terms then it would
2159					be a good idea to read at least the following perl manuals first:
2160					L<perlreftut>, L<perldsc>, L<perllol>, and L<perlboot>.
2161
2162
2163					=head2 Architecture of a DBI Application
2164
2165					\|<- Scope of DBI ->\|
2166					.-. .--------------. .-------------.
2167					.-------. \| \|---\| XYZ Driver \|---\| XYZ Engine \|
2168					\| Perl \| \| \| `--------------' `-------------'
2169					\| script\| \|A\| \|D\| .--------------. .-------------.
2170					\| using \|--\|P\|--\|B\|---\|Oracle Driver \|---\|Oracle Engine\|
2171					\| DBI \| \|I\| \|I\| `--------------' `-------------'
2172					\| API \| \| \|...
2173					\|methods\| \| \|... Other drivers
2174					`-------' \| \|...
2175					`-'
2176
2177					The API, or Application Programming Interface, defines the
2178					call interface and variables for Perl scripts to use. The API
2179					is implemented by the Perl DBI extension.
2180
2181					The DBI "dispatches" the method calls to the appropriate driver for
2182					actual execution. The DBI is also responsible for the dynamic loading
2183					of drivers, error checking and handling, providing default
2184					implementations for methods, and many other non-database specific duties.
2185
2186					Each driver
2187					contains implementations of the DBI methods using the
2188					private interface functions of the corresponding database engine. Only authors
2189					of sophisticated/multi-database applications or generic library
2190					functions need be concerned with drivers.
2191
2192					=head2 Notation and Conventions
2193
2194					The following conventions are used in this document:
2195
2196					$dbh Database handle object
2197					$sth Statement handle object
2198					$drh Driver handle object (rarely seen or used in applications)
2199					$h Any of the handle types above ($dbh, $sth, or $drh)
2200					$rc General Return Code (boolean: true=ok, false=error)
2201					$rv General Return Value (typically an integer)
2202					@ary List of values returned from the database, typically a row of data
2203					$rows Number of rows processed (if available, else -1)
2204					$fh A filehandle
2205					undef NULL values are represented by undefined values in Perl
2206					\%attr Reference to a hash of attribute values passed to methods
2207
2208					Note that Perl will automatically destroy database and statement handle objects
2209					if all references to them are deleted.
2210
2211
2212					=head2 Outline Usage
2213
2214					To use DBI,
2215					first you need to load the DBI module:
2216
2217					use DBI;
2218					use strict;
2219
2220					(The C<use strict;> isn't required but is strongly recommended.)
2221
2222					Then you need to L</connect> to your data source and get a I<handle> for that
2223					connection:
2224
2225					$dbh = DBI->connect($dsn, $user, $password,
2226					{ RaiseError => 1, AutoCommit => 0 });
2227
2228					Since connecting can be expensive, you generally just connect at the
2229					start of your program and disconnect at the end.
2230
2231					Explicitly defining the required C<AutoCommit> behaviour is strongly
2232					recommended and may become mandatory in a later version. This
2233					determines whether changes are automatically committed to the
2234					database when executed, or need to be explicitly committed later.
2235
2236					The DBI allows an application to "prepare" statements for later
2237					execution. A prepared statement is identified by a statement handle
2238					held in a Perl variable.
2239					We'll call the Perl variable C<$sth> in our examples.
2240
2241					The typical method call sequence for a C<SELECT> statement is:
2242
2243					prepare,
2244					execute, fetch, fetch, ...
2245					execute, fetch, fetch, ...
2246					execute, fetch, fetch, ...
2247
2248					for example:
2249
2250					$sth = $dbh->prepare("SELECT foo, bar FROM table WHERE baz=?");
2251
2252					$sth->execute( $baz );
2253
2254					while ( @row = $sth->fetchrow_array ) {
2255					print "@row\n";
2256					}
2257
2258					The typical method call sequence for a I<non>-C<SELECT> statement is:
2259
2260					prepare,
2261					execute,
2262					execute,
2263					execute.
2264
2265					for example:
2266
2267					$sth = $dbh->prepare("INSERT INTO table(foo,bar,baz) VALUES (?,?,?)");
2268
2269					while(<CSV>) {
2270					chomp;
2271					my ($foo,$bar,$baz) = split /,/;
2272					$sth->execute( $foo, $bar, $baz );
2273					}
2274
2275					The C<do()> method can be used for non repeated I<non>-C<SELECT> statement
2276					(or with drivers that don't support placeholders):
2277
2278					$rows_affected = $dbh->do("UPDATE your_table SET foo = foo + 1");
2279
2280					To commit your changes to the database (when L</AutoCommit> is off):
2281
2282					$dbh->commit; # or call $dbh->rollback; to undo changes
2283
2284					Finally, when you have finished working with the data source, you should
2285					L</disconnect> from it:
2286
2287					$dbh->disconnect;
2288
2289
2290					=head2 General Interface Rules & Caveats
2291
2292					The DBI does not have a concept of a "current session". Every session
2293					has a handle object (i.e., a C<$dbh>) returned from the C<connect> method.
2294					That handle object is used to invoke database related methods.
2295
2296					Most data is returned to the Perl script as strings. (Null values are
2297					returned as C<undef>.) This allows arbitrary precision numeric data to be
2298					handled without loss of accuracy. Beware that Perl may not preserve
2299					the same accuracy when the string is used as a number.
2300
2301					Dates and times are returned as character strings in the current
2302					default format of the corresponding database engine. Time zone effects
2303					are database/driver dependent.
2304
2305					Perl supports binary data in Perl strings, and the DBI will pass binary
2306					data to and from the driver without change. It is up to the driver
2307					implementors to decide how they wish to handle such binary data.
2308
2309					Perl supports two kinds of strings: Unicode (utf8 internally) and non-Unicode
2310					(defaults to iso-8859-1 if forced to assume an encoding). Drivers should
2311					accept both kinds of strings and, if required, convert them to the character
2312					set of the database being used. Similarly, when fetching from the database
2313					character data that isn't iso-8859-1 the driver should convert it into utf8.
2314
2315					Multiple SQL statements may not be combined in a single statement
2316					handle (C<$sth>), although some databases and drivers do support this
2317					(notably Sybase and SQL Server).
2318
2319					Non-sequential record reads are not supported in this version of the DBI.
2320					In other words, records can only be fetched in the order that the
2321					database returned them, and once fetched they are forgotten.
2322
2323					Positioned updates and deletes are not directly supported by the DBI.
2324					See the description of the C<CursorName> attribute for an alternative.
2325
2326					Individual driver implementors are free to provide any private
2327					functions and/or handle attributes that they feel are useful.
2328					Private driver functions can be invoked using the DBI C<func()> method.
2329					Private driver attributes are accessed just like standard attributes.
2330
2331					Many methods have an optional C<\%attr> parameter which can be used to
2332					pass information to the driver implementing the method. Except where
2333					specifically documented, the C<\%attr> parameter can only be used to pass
2334					driver specific hints. In general, you can ignore C<\%attr> parameters
2335					or pass it as C<undef>.
2336
2337
2338					=head2 Naming Conventions and Name Space
2339
2340					The DBI package and all packages below it (C<DBI::*>) are reserved for
2341					use by the DBI. Extensions and related modules use the C<DBIx::>
2342					namespace (see L<http://www.perl.com/CPAN/modules/by-module/DBIx/>).
2343					Package names beginning with C<DBD::> are reserved for use
2344					by DBI database drivers. All environment variables used by the DBI
2345					or by individual DBDs begin with "C<DBI_>" or "C<DBD_>".
2346
2347					The letter case used for attribute names is significant and plays an
2348					important part in the portability of DBI scripts. The case of the
2349					attribute name is used to signify who defined the meaning of that name
2350					and its values.
2351
2352					Case of name Has a meaning defined by
2353					------------ ------------------------
2354					UPPER_CASE Standards, e.g., X/Open, ISO SQL92 etc (portable)
2355					MixedCase DBI API (portable), underscores are not used.
2356					lower_case Driver or database engine specific (non-portable)
2357
2358					It is of the utmost importance that Driver developers only use
2359					lowercase attribute names when defining private attributes. Private
2360					attribute names must be prefixed with the driver name or suitable
2361					abbreviation (e.g., "C<ora_>" for Oracle, "C<ing_>" for Ingres, etc).
2362
2363
2364					=head2 SQL - A Query Language
2365
2366					Most DBI drivers require applications to use a dialect of SQL
2367					(Structured Query Language) to interact with the database engine.
2368					The L</"Standards Reference Information"> section provides links
2369					to useful information about SQL.
2370
2371					The DBI itself does not mandate or require any particular language to
2372					be used; it is language independent. In ODBC terms, the DBI is in
2373					"pass-thru" mode, although individual drivers might not be. The only requirement
2374					is that queries and other statements must be expressed as a single
2375					string of characters passed as the first argument to the L</prepare> or
2376					L</do> methods.
2377
2378					For an interesting diversion on the I<real> history of RDBMS and SQL,
2379					from the people who made it happen, see:
2380
2381					http://www.mcjones.org/System_R/SQL_Reunion_95/sqlr95.html
2382
2383					Follow the "Full Contents" then "Intergalactic dataspeak" links for the
2384					SQL history.
2385
2386					=head2 Placeholders and Bind Values
2387
2388					Some drivers support placeholders and bind values.
2389					I<Placeholders>, also called parameter markers, are used to indicate
2390					values in a database statement that will be supplied later,
2391					before the prepared statement is executed. For example, an application
2392					might use the following to insert a row of data into the SALES table:
2393
2394					INSERT INTO sales (product_code, qty, price) VALUES (?, ?, ?)
2395
2396					or the following, to select the description for a product:
2397
2398					SELECT description FROM products WHERE product_code = ?
2399
2400					The C<?> characters are the placeholders. The association of actual
2401					values with placeholders is known as I<binding>, and the values are
2402					referred to as I<bind values>.
2403					Note that the C<?> is not enclosed in quotation marks, even when the
2404					placeholder represents a string.
2405
2406					Some drivers also allow placeholders like C<:>I<name> and C<:>I<N> (e.g.,
2407					C<:1>, C<:2>, and so on) in addition to C<?>, but their use is not portable.
2408
2409					If the C<:>I<N> form of placeholder is supported by the driver you're using,
2410					then you should be able to use either L</bind_param> or L</execute> to bind
2411					values. Check your driver documentation.
2412
2413					With most drivers, placeholders can't be used for any element of a
2414					statement that would prevent the database server from validating the
2415					statement and creating a query execution plan for it. For example:
2416
2417					"SELECT name, age FROM ?" # wrong (will probably fail)
2418					"SELECT name, ? FROM people" # wrong (but may not 'fail')
2419
2420					Also, placeholders can only represent single scalar values.
2421					For example, the following
2422					statement won't work as expected for more than one value:
2423
2424					"SELECT name, age FROM people WHERE name IN (?)" # wrong
2425					"SELECT name, age FROM people WHERE name IN (?,?)" # two names
2426
2427					When using placeholders with the SQL C<LIKE> qualifier, you must
2428					remember that the placeholder substitutes for the whole string.
2429					So you should use "C<... LIKE ? ...>" and include any wildcard
2430					characters in the value that you bind to the placeholder.
2431
2432					B<NULL Values>
2433
2434					Undefined values, or C<undef>, are used to indicate NULL values.
2435					You can insert and update columns with a NULL value as you would a
2436					non-NULL value. These examples insert and update the column
2437					C<age> with a NULL value:
2438
2439					$sth = $dbh->prepare(qq{
2440					INSERT INTO people (fullname, age) VALUES (?, ?)
2441					});
2442					$sth->execute("Joe Bloggs", undef);
2443
2444					$sth = $dbh->prepare(qq{
2445					UPDATE people SET age = ? WHERE fullname = ?
2446					});
2447					$sth->execute(undef, "Joe Bloggs");
2448
2449					However, care must be taken when trying to use NULL values in a
2450					C<WHERE> clause. Consider:
2451
2452					SELECT fullname FROM people WHERE age = ?
2453
2454					Binding an C<undef> (NULL) to the placeholder will I<not> select rows
2455					which have a NULL C<age>! At least for database engines that
2456					conform to the SQL standard. Refer to the SQL manual for your database
2457					engine or any SQL book for the reasons for this. To explicitly select
2458					NULLs you have to say "C<WHERE age IS NULL>".
2459
2460					A common issue is to have a code fragment handle a value that could be
2461					either C<defined> or C<undef> (non-NULL or NULL) at runtime.
2462					A simple technique is to prepare the appropriate statement as needed,
2463					and substitute the placeholder for non-NULL cases:
2464
2465					$sql_clause = defined $age? "age = ?" : "age IS NULL";
2466					$sth = $dbh->prepare(qq{
2467					SELECT fullname FROM people WHERE $sql_clause
2468					});
2469					$sth->execute(defined $age ? $age : ());
2470
2471					The following technique illustrates qualifying a C<WHERE> clause with
2472					several columns, whose associated values (C<defined> or C<undef>) are
2473					in a hash %h:
2474
2475					for my $col ("age", "phone", "email") {
2476					if (defined $h{$col}) {
2477					push @sql_qual, "$col = ?";
2478					push @sql_bind, $h{$col};
2479					}
2480					else {
2481					push @sql_qual, "$col IS NULL";
2482					}
2483					}
2484					$sql_clause = join(" AND ", @sql_qual);
2485					$sth = $dbh->prepare(qq{
2486					SELECT fullname FROM people WHERE $sql_clause
2487					});
2488					$sth->execute(@sql_bind);
2489
2490					The techniques above call prepare for the SQL statement with each call to
2491					execute. Because calls to prepare() can be expensive, performance
2492					can suffer when an application iterates many times over statements
2493					like the above.
2494
2495					A better solution is a single C<WHERE> clause that supports both
2496					NULL and non-NULL comparisons. Its SQL statement would need to be
2497					prepared only once for all cases, thus improving performance.
2498					Several examples of C<WHERE> clauses that support this are presented
2499					below. But each example lacks portability, robustness, or simplicity.
2500					Whether an example is supported on your database engine depends on
2501					what SQL extensions it provides, and where it supports the C<?>
2502					placeholder in a statement.
2503
2504					0) age = ?
2505					1) NVL(age, xx) = NVL(?, xx)
2506					2) ISNULL(age, xx) = ISNULL(?, xx)
2507					3) DECODE(age, ?, 1, 0) = 1
2508					4) age = ? OR (age IS NULL AND ? IS NULL)
2509					5) age = ? OR (age IS NULL AND SP_ISNULL(?) = 1)
2510					6) age = ? OR (age IS NULL AND ? = 1)
2511
2512					Statements formed with the above C<WHERE> clauses require execute
2513					statements as follows. The arguments are required, whether their
2514					values are C<defined> or C<undef>.
2515
2516					0,1,2,3) $sth->execute($age);
2517					4,5) $sth->execute($age, $age);
2518					6) $sth->execute($age, defined($age) ? 0 : 1);
2519
2520					Example 0 should not work (as mentioned earlier), but may work on
2521					a few database engines anyway (e.g. Sybase). Example 0 is part
2522					of examples 4, 5, and 6, so if example 0 works, these other
2523					examples may work, even if the engine does not properly support
2524					the right hand side of the C<OR> expression.
2525
2526					Examples 1 and 2 are not robust: they require that you provide a
2527					valid column value xx (e.g. '~') which is not present in any row.
2528					That means you must have some notion of what data won't be stored
2529					in the column, and expect clients to adhere to that.
2530
2531					Example 5 requires that you provide a stored procedure (SP_ISNULL
2532					in this example) that acts as a function: it checks whether a value
2533					is null, and returns 1 if it is, or 0 if not.
2534
2535					Example 6, the least simple, is probably the most portable, i.e., it
2536					should work with most, if not all, database engines.
2537
2538					Here is a table that indicates which examples above are known to
2539					work on various database engines:
2540
2541					-----Examples------
2542					0 1 2 3 4 5 6
2543					- - - - - - -
2544					Oracle 9 N Y N Y Y ? Y
2545					Informix IDS 9 N N N Y N Y Y
2546					MS SQL N N Y N Y ? Y
2547					Sybase Y N N N N N Y
2548					AnyData,DBM,CSV Y N N N Y Y* Y
2549					SQLite 3.3 N N N N Y N N
2550					MSAccess N N N N Y N Y
2551
2552					* Works only because Example 0 works.
2553
2554					DBI provides a sample perl script that will test the examples above
2555					on your database engine and tell you which ones work. It is located
2556					in the F<ex/> subdirectory of the DBI source distribution, or here:
2557					L<https://github.com/perl5-dbi/dbi/blob/master/ex/perl_dbi_nulls_test.pl>
2558					Please use the script to help us fill-in and maintain this table.
2559
2560					B<Performance>
2561
2562					Without using placeholders, the insert statement shown previously would have to
2563					contain the literal values to be inserted and would have to be
2564					re-prepared and re-executed for each row. With placeholders, the insert
2565					statement only needs to be prepared once. The bind values for each row
2566					can be given to the C<execute> method each time it's called. By avoiding
2567					the need to re-prepare the statement for each row, the application
2568					typically runs many times faster. Here's an example:
2569
2570					my $sth = $dbh->prepare(q{
2571					INSERT INTO sales (product_code, qty, price) VALUES (?, ?, ?)
2572					}) or die $dbh->errstr;
2573					while (<>) {
2574					chomp;
2575					my ($product_code, $qty, $price) = split /,/;
2576					$sth->execute($product_code, $qty, $price) or die $dbh->errstr;
2577					}
2578					$dbh->commit or die $dbh->errstr;
2579
2580					See L</execute> and L</bind_param> for more details.
2581
2582					The C<q{...}> style quoting used in this example avoids clashing with
2583					quotes that may be used in the SQL statement. Use the double-quote like
2584					C<qq{...}> operator if you want to interpolate variables into the string.
2585					See L<perlop/"Quote and Quote-like Operators"> for more details.
2586
2587					See also the L</bind_columns> method, which is used to associate Perl
2588					variables with the output columns of a C<SELECT> statement.
2589
2590					=head1 THE DBI PACKAGE AND CLASS
2591
2592					In this section, we cover the DBI class methods, utility functions,
2593					and the dynamic attributes associated with generic DBI handles.
2594
2595					=head2 DBI Constants
2596
2597					Constants representing the values of the SQL standard types can be
2598					imported individually by name, or all together by importing the
2599					special C<:sql_types> tag.
2600
2601					The names and values of all the defined SQL standard types can be
2602					produced like this:
2603
2604					foreach (@{ $DBI::EXPORT_TAGS{sql_types} }) {
2605					printf "%s=%d\n", $_, &{"DBI::$_"};
2606					}
2607
2608					These constants are defined by SQL/CLI, ODBC or both.
2609					C<SQL_BIGINT> has conflicting codes in SQL/CLI and ODBC,
2610					DBI uses the ODBC one.
2611
2612					See the L</type_info>, L</type_info_all>, and L</bind_param> methods
2613					for possible uses.
2614
2615					Note that just because the DBI defines a named constant for a given
2616					data type doesn't mean that drivers will support that data type.
2617
2618
2619					=head2 DBI Class Methods
2620
2621					The following methods are provided by the DBI class:
2622
2623					=head3 C<parse_dsn>
2624
2625					($scheme, $driver, $attr_string, $attr_hash, $driver_dsn) = DBI->parse_dsn($dsn)
2626					or die "Can't parse DBI DSN '$dsn'";
2627
2628					Breaks apart a DBI Data Source Name (DSN) and returns the individual
2629					parts. If $dsn doesn't contain a valid DSN then parse_dsn() returns
2630					an empty list.
2631
2632					$scheme is the first part of the DSN and is currently always 'dbi'.
2633					$driver is the driver name, possibly defaulted to $ENV{DBI_DRIVER},
2634					and may be undefined. $attr_string is the contents of the optional attribute
2635					string, which may be undefined. If $attr_string is not empty then $attr_hash
2636					is a reference to a hash containing the parsed attribute names and values.
2637					$driver_dsn is the last part of the DBI DSN string. For example:
2638
2639					($scheme, $driver, $attr_string, $attr_hash, $driver_dsn)
2640					= DBI->parse_dsn("DBI:MyDriver(RaiseError=>1):db=test;port=42");
2641					$scheme = 'dbi';
2642					$driver = 'MyDriver';
2643					$attr_string = 'RaiseError=>1';
2644					$attr_hash = { 'RaiseError' => '1' };
2645					$driver_dsn = 'db=test;port=42';
2646
2647					The parse_dsn() method was added in DBI 1.43.
2648
2649					=head3 C<connect>
2650
2651					$dbh = DBI->connect($data_source, $username, $password)
2652					or die $DBI::errstr;
2653					$dbh = DBI->connect($data_source, $username, $password, \%attr)
2654					or die $DBI::errstr;
2655
2656					Establishes a database connection, or session, to the requested C<$data_source>.
2657					Returns a database handle object if the connection succeeds. Use
2658					C<$dbh-E<gt>disconnect> to terminate the connection.
2659
2660					If the connect fails (see below), it returns C<undef> and sets both C<$DBI::err>
2661					and C<$DBI::errstr>. (It does I<not> explicitly set C<$!>.) You should generally
2662					test the return status of C<connect> and C<print $DBI::errstr> if it has failed.
2663
2664					Multiple simultaneous connections to multiple databases through multiple
2665					drivers can be made via the DBI. Simply make one C<connect> call for each
2666					database and keep a copy of each returned database handle.
2667
2668					The C<$data_source> value must begin with "C<dbi:>I<driver_name>C<:>".
2669					The I<driver_name> specifies the driver that will be used to make the
2670					connection. (Letter case is significant.)
2671
2672					As a convenience, if the C<$data_source> parameter is undefined or empty,
2673					the DBI will substitute the value of the environment variable C<DBI_DSN>.
2674					If just the I<driver_name> part is empty (i.e., the C<$data_source>
2675					prefix is "C<dbi::>"), the environment variable C<DBI_DRIVER> is
2676					used. If neither variable is set, then C<connect> dies.
2677
2678					Examples of C<$data_source> values are:
2679
2680					dbi:DriverName:database_name
2681					dbi:DriverName:database_name@hostname:port
2682					dbi:DriverName:database=database_name;host=hostname;port=port
2683
2684					There is I<no standard> for the text following the driver name. Each
2685					driver is free to use whatever syntax it wants. The only requirement the
2686					DBI makes is that all the information is supplied in a single string.
2687					You must consult the documentation for the drivers you are using for a
2688					description of the syntax they require.
2689
2690					It is recommended that drivers support the ODBC style, shown in the
2691					last example above. It is also recommended that they support the
2692					three common names 'C<host>', 'C<port>', and 'C<database>' (plus 'C<db>'
2693					as an alias for C<database>). This simplifies automatic construction
2694					of basic DSNs: C<"dbi:$driver:database=$db;host=$host;port=$port">.
2695					Drivers should aim to 'do something reasonable' when given a DSN
2696					in this form, but if any part is meaningless for that driver (such
2697					as 'port' for Informix) it should generate an error if that part
2698					is not empty.
2699
2700					If the environment variable C<DBI_AUTOPROXY> is defined (and the
2701					driver in C<$data_source> is not "C<Proxy>") then the connect request
2702					will automatically be changed to:
2703
2704					$ENV{DBI_AUTOPROXY};dsn=$data_source
2705
2706					C<DBI_AUTOPROXY> is typically set as "C<dbi:Proxy:hostname=...;port=...>".
2707					If $ENV{DBI_AUTOPROXY} doesn't begin with 'C<dbi:>' then "dbi:Proxy:"
2708					will be prepended to it first. See the DBD::Proxy documentation
2709					for more details.
2710
2711					If C<$username> or C<$password> are undefined (rather than just empty),
2712					then the DBI will substitute the values of the C<DBI_USER> and C<DBI_PASS>
2713					environment variables, respectively. The DBI will warn if the
2714					environment variables are not defined. However, the everyday use
2715					of these environment variables is not recommended for security
2716					reasons. The mechanism is primarily intended to simplify testing.
2717					See below for alternative way to specify the username and password.
2718
2719					C<DBI-E<gt>connect> automatically installs the driver if it has not been
2720					installed yet. Driver installation either returns a valid driver
2721					handle, or it I<dies> with an error message that includes the string
2722					"C<install_driver>" and the underlying problem. So C<DBI-E<gt>connect>
2723					will die
2724					on a driver installation failure and will only return C<undef> on a
2725					connect failure, in which case C<$DBI::errstr> will hold the error message.
2726					Use C<eval { ... }> if you need to catch the "C<install_driver>" error.
2727
2728					The C<$data_source> argument (with the "C<dbi:...:>" prefix removed) and the
2729					C<$username> and C<$password> arguments are then passed to the driver for
2730					processing. The DBI does not define any interpretation for the
2731					contents of these fields. The driver is free to interpret the
2732					C<$data_source>, C<$username>, and C<$password> fields in any way, and supply
2733					whatever defaults are appropriate for the engine being accessed.
2734					(Oracle, for example, uses the ORACLE_SID and TWO_TASK environment
2735					variables if no C<$data_source> is specified.)
2736
2737					The C<AutoCommit> and C<PrintError> attributes for each connection
2738					default to "on". (See L</AutoCommit> and L</PrintError> for more information.)
2739					However, it is strongly recommended that you explicitly define C<AutoCommit>
2740					rather than rely on the default. The C<PrintWarn> attribute defaults to true.
2741
2742					The C<\%attr> parameter can be used to alter the default settings of
2743					C<PrintError>, C<RaiseError>, C<AutoCommit>, and other attributes. For example:
2744
2745					$dbh = DBI->connect($data_source, $user, $pass, {
2746					PrintError => 0,
2747					AutoCommit => 0
2748					});
2749
2750					The username and password can also be specified using the attributes
2751					C<Username> and C<Password>, in which case they take precedence
2752					over the C<$username> and C<$password> parameters.
2753
2754					You can also define connection attribute values within the C<$data_source>
2755					parameter. For example:
2756
2757					dbi:DriverName(PrintWarn=>0,PrintError=>0,Taint=>1):...
2758
2759					Individual attributes values specified in this way take precedence over
2760					any conflicting values specified via the C<\%attr> parameter to C<connect>.
2761
2762					The C<dbi_connect_method> attribute can be used to specify which driver
2763					method should be called to establish the connection. The only useful
2764					values are 'connect', 'connect_cached', or some specialized case like
2765					'Apache::DBI::connect' (which is automatically the default when running
2766					within Apache).
2767
2768					Where possible, each session (C<$dbh>) is independent from the transactions
2769					in other sessions. This is useful when you need to hold cursors open
2770					across transactions--for example, if you use one session for your long lifespan
2771					cursors (typically read-only) and another for your short update
2772					transactions.
2773
2774					For compatibility with old DBI scripts, the driver can be specified by
2775					passing its name as the fourth argument to C<connect> (instead of C<\%attr>):
2776
2777					$dbh = DBI->connect($data_source, $user, $pass, $driver);
2778
2779					In this "old-style" form of C<connect>, the C<$data_source> should not start
2780					with "C<dbi:driver_name:>". (If it does, the embedded driver_name
2781					will be ignored). Also note that in this older form of C<connect>,
2782					the C<$dbh-E<gt>{AutoCommit}> attribute is I<undefined>, the
2783					C<$dbh-E<gt>{PrintError}> attribute is off, and the old C<DBI_DBNAME>
2784					environment variable is
2785					checked if C<DBI_DSN> is not defined. Beware that this "old-style"
2786					C<connect> will soon be withdrawn in a future version of DBI.
2787
2788					=head3 C<connect_cached>
2789
2790					$dbh = DBI->connect_cached($data_source, $username, $password)
2791					or die $DBI::errstr;
2792					$dbh = DBI->connect_cached($data_source, $username, $password, \%attr)
2793					or die $DBI::errstr;
2794
2795					C<connect_cached> is like L</connect>, except that the database handle
2796					returned is also
2797					stored in a hash associated with the given parameters. If another call
2798					is made to C<connect_cached> with the same parameter values, then the
2799					corresponding cached C<$dbh> will be returned if it is still valid.
2800					The cached database handle is replaced with a new connection if it
2801					has been disconnected or if the C<ping> method fails.
2802
2803					Note that the behaviour of this method differs in several respects from the
2804					behaviour of persistent connections implemented by Apache::DBI.
2805					However, if Apache::DBI is loaded then C<connect_cached> will use it.
2806
2807					Caching connections can be useful in some applications, but it can
2808					also cause problems, such as too many connections, and so should
2809					be used with care. In particular, avoid changing the attributes of
2810					a database handle created via connect_cached() because it will affect
2811					other code that may be using the same handle. When connect_cached()
2812					returns a handle the attributes will be reset to their initial values.
2813					This can cause problems, especially with the C<AutoCommit> attribute.
2814
2815					Also, to ensure that the attributes passed are always the same, avoid passing
2816					references inline. For example, the C<Callbacks> attribute is specified as a
2817					hash reference. Be sure to declare it external to the call to
2818					connect_cached(), such that the hash reference is not re-created on every
2819					call. A package-level lexical works well:
2820
2821					package MyDBH;
2822					my $cb = {
2823					'connect_cached.reused' => sub { delete $_[4]->{AutoCommit} },
2824					};
2825
2826					sub dbh {
2827					DBI->connect_cached( $dsn, $username, $auth, { Callbacks => $cb });
2828					}
2829
2830					Where multiple separate parts of a program are using connect_cached()
2831					to connect to the same database with the same (initial) attributes
2832					it is a good idea to add a private attribute to the connect_cached()
2833					call to effectively limit the scope of the caching. For example:
2834
2835					DBI->connect_cached(..., { private_foo_cachekey => "Bar", ... });
2836
2837					Handles returned from that connect_cached() call will only be returned
2838					by other connect_cached() call elsewhere in the code if those other
2839					calls also pass in the same attribute values, including the private one.
2840					(I've used C<private_foo_cachekey> here as an example, you can use
2841					any attribute name with a C<private_> prefix.)
2842
2843					Taking that one step further, you can limit a particular connect_cached()
2844					call to return handles unique to that one place in the code by setting the
2845					private attribute to a unique value for that place:
2846
2847					DBI->connect_cached(..., { private_foo_cachekey => __FILE__.__LINE__, ... });
2848
2849					By using a private attribute you still get connection caching for
2850					the individual calls to connect_cached() but, by making separate
2851					database connections for separate parts of the code, the database
2852					handles are isolated from any attribute changes made to other handles.
2853
2854					The cache can be accessed (and cleared) via the L</CachedKids> attribute:
2855
2856					my $CachedKids_hashref = $dbh->{Driver}->{CachedKids};
2857					%$CachedKids_hashref = () if $CachedKids_hashref;
2858
2859
2860					=head3 C<available_drivers>
2861
2862					@ary = DBI->available_drivers;
2863					@ary = DBI->available_drivers($quiet);
2864
2865					Returns a list of all available drivers by searching for C<DBD::*> modules
2866					through the directories in C<@INC>. By default, a warning is given if
2867					some drivers are hidden by others of the same name in earlier
2868					directories. Passing a true value for C<$quiet> will inhibit the warning.
2869
2870					=head3 C<installed_drivers>
2871
2872					%drivers = DBI->installed_drivers();
2873
2874					Returns a list of driver name and driver handle pairs for all drivers
2875					'installed' (loaded) into the current process. The driver name does not
2876					include the 'DBD::' prefix.
2877
2878					To get a list of all drivers available in your perl installation you can use
2879					L</available_drivers>.
2880
2881					Added in DBI 1.49.
2882
2883					=head3 C<installed_versions>
2884
2885					DBI->installed_versions;
2886					@ary = DBI->installed_versions;
2887					$hash = DBI->installed_versions;
2888
2889					Calls available_drivers() and attempts to load each of them in turn
2890					using install_driver(). For each load that succeeds the driver
2891					name and version number are added to a hash. When running under
2892					L<DBI::PurePerl> drivers which appear not be pure-perl are ignored.
2893
2894					When called in array context the list of successfully loaded drivers
2895					is returned (without the 'DBD::' prefix).
2896
2897					When called in scalar context an extra entry for the C<DBI> is added (and
2898					C<DBI::PurePerl> if appropriate) and a reference to the hash is returned.
2899
2900					When called in a void context the installed_versions() method will
2901					print out a formatted list of the hash contents, one per line, along with some
2902					other information about the DBI version and OS.
2903
2904					Due to the potentially high memory cost and unknown risks of loading
2905					in an unknown number of drivers that just happen to be installed
2906					on the system, this method is not recommended for general use.
2907					Use available_drivers() instead.
2908
2909					The installed_versions() method is primarily intended as a quick
2910					way to see from the command line what's installed. For example:
2911
2912					perl -MDBI -e 'DBI->installed_versions'
2913
2914					The installed_versions() method was added in DBI 1.38.
2915
2916					=head3 C<data_sources>
2917
2918					@ary = DBI->data_sources($driver);
2919					@ary = DBI->data_sources($driver, \%attr);
2920
2921					Returns a list of data sources (databases) available via the named
2922					driver. If C<$driver> is empty or C<undef>, then the value of the
2923					C<DBI_DRIVER> environment variable is used.
2924
2925					The driver will be loaded if it hasn't been already. Note that if the
2926					driver loading fails then data_sources() I<dies> with an error message
2927					that includes the string "C<install_driver>" and the underlying problem.
2928
2929					Data sources are returned in a form suitable for passing to the
2930					L</connect> method (that is, they will include the "C<dbi:$driver:>" prefix).
2931
2932					Note that many drivers have no way of knowing what data sources might
2933					be available for it. These drivers return an empty or incomplete list
2934					or may require driver-specific attributes.
2935
2936					There is also a data_sources() method defined for database handles.
2937
2938
2939					=head3 C<trace>
2940
2941					DBI->trace($trace_setting)
2942					DBI->trace($trace_setting, $trace_filename)
2943					DBI->trace($trace_setting, $trace_filehandle)
2944					$trace_setting = DBI->trace;
2945
2946					The C<DBI-E<gt>trace> method sets the I<global default> trace
2947					settings and returns the I<previous> trace settings. It can also
2948					be used to change where the trace output is sent.
2949
2950					There's a similar method, C<$h-E<gt>trace>, which sets the trace
2951					settings for the specific handle it's called on.
2952
2953					See the L</TRACING> section for full details about the DBI's powerful
2954					tracing facilities.
2955
2956
2957					=head3 C<visit_handles>
2958
2959					DBI->visit_handles( $coderef );
2960					DBI->visit_handles( $coderef, $info );
2961
2962					Where $coderef is a reference to a subroutine and $info is an arbitrary value
2963					which, if undefined, defaults to a reference to an empty hash. Returns $info.
2964
2965					For each installed driver handle, if any, $coderef is invoked as:
2966
2967					$coderef->($driver_handle, $info);
2968
2969					If the execution of $coderef returns a true value then L</visit_child_handles>
2970					is called on that child handle and passed the returned value as $info.
2971
2972					For example:
2973
2974					my $info = $dbh->{Driver}->visit_child_handles(sub {
2975					my ($h, $info) = @_;
2976					++$info->{ $h->{Type} }; # count types of handles (dr/db/st)
2977					return $info; # visit kids
2978					});
2979
2980					See also L</visit_child_handles>.
2981
2982					=head2 DBI Utility Functions
2983
2984					In addition to the DBI methods listed in the previous section,
2985					the DBI package also provides several utility functions.
2986
2987					These can be imported into your code by listing them in
2988					the C<use> statement. For example:
2989
2990					use DBI qw(neat data_diff);
2991
2992					Alternatively, all these utility functions (except hash) can be
2993					imported using the C<:utils> import tag. For example:
2994
2995					use DBI qw(:utils);
2996
2997					=head3 C<data_string_desc>
2998
2999					$description = data_string_desc($string);
3000
3001					Returns an informal description of the string. For example:
3002
3003					UTF8 off, ASCII, 42 characters 42 bytes
3004					UTF8 off, non-ASCII, 42 characters 42 bytes
3005					UTF8 on, non-ASCII, 4 characters 6 bytes
3006					UTF8 on but INVALID encoding, non-ASCII, 4 characters 6 bytes
3007					UTF8 off, undef
3008
3009					The initial C<UTF8> on/off refers to Perl's internal SvUTF8 flag.
3010					If $string has the SvUTF8 flag set but the sequence of bytes it
3011					contains are not a valid UTF-8 encoding then data_string_desc()
3012					will report C<UTF8 on but INVALID encoding>.
3013
3014					The C<ASCII> vs C<non-ASCII> portion shows C<ASCII> if I<all> the
3015					characters in the string are ASCII (have code points <= 127).
3016
3017					The data_string_desc() function was added in DBI 1.46.
3018
3019					=head3 C<data_string_diff>
3020
3021					$diff = data_string_diff($a, $b);
3022
3023					Returns an informal description of the first character difference
3024					between the strings. If both $a and $b contain the same sequence
3025					of characters then data_string_diff() returns an empty string.
3026					For example:
3027
3028					Params a & b Result
3029					------------ ------
3030					'aaa', 'aaa' ''
3031					'aaa', 'abc' 'Strings differ at index 2: a[2]=a, b[2]=b'
3032					'aaa', undef 'String b is undef, string a has 3 characters'
3033					'aaa', 'aa' 'String b truncated after 2 characters'
3034
3035					Unicode characters are reported in C<\x{XXXX}> format. Unicode
3036					code points in the range U+0800 to U+08FF are unassigned and most
3037					likely to occur due to double-encoding. Characters in this range
3038					are reported as C<\x{08XX}='C'> where C<C> is the corresponding
3039					latin-1 character.
3040
3041					The data_string_diff() function only considers logical I<characters>
3042					and not the underlying encoding. See L</data_diff> for an alternative.
3043
3044					The data_string_diff() function was added in DBI 1.46.
3045
3046					=head3 C<data_diff>
3047
3048					$diff = data_diff($a, $b);
3049					$diff = data_diff($a, $b, $logical);
3050
3051					Returns an informal description of the difference between two strings.
3052					It calls L</data_string_desc> and L</data_string_diff>
3053					and returns the combined results as a multi-line string.
3054
3055					For example, C<data_diff("abc", "ab\x{263a}")> will return:
3056
3057					a: UTF8 off, ASCII, 3 characters 3 bytes
3058					b: UTF8 on, non-ASCII, 3 characters 5 bytes
3059					Strings differ at index 2: a[2]=c, b[2]=\x{263A}
3060
3061					If $a and $b are identical in both the characters they contain I<and>
3062					their physical encoding then data_diff() returns an empty string.
3063					If $logical is true then physical encoding differences are ignored
3064					(but are still reported if there is a difference in the characters).
3065
3066					The data_diff() function was added in DBI 1.46.
3067
3068					=head3 C<neat>
3069
3070					$str = neat($value);
3071					$str = neat($value, $maxlen);
3072
3073					Return a string containing a neat (and tidy) representation of the
3074					supplied value.
3075
3076					Strings will be quoted, although internal quotes will I<not> be escaped.
3077					Values known to be numeric will be unquoted. Undefined (NULL) values
3078					will be shown as C<undef> (without quotes).
3079
3080					If the string is flagged internally as utf8 then double quotes will
3081					be used, otherwise single quotes are used and unprintable characters
3082					will be replaced by dot (.).
3083
3084					For result strings longer than C<$maxlen> the result string will be
3085					truncated to C<$maxlen-4> and "C<...'>" will be appended. If C<$maxlen> is 0
3086					or C<undef>, it defaults to C<$DBI::neat_maxlen> which, in turn, defaults to 400.
3087
3088					This function is designed to format values for human consumption.
3089					It is used internally by the DBI for L</trace> output. It should
3090					typically I<not> be used for formatting values for database use.
3091					(See also L</quote>.)
3092
3093					=head3 C<neat_list>
3094
3095					$str = neat_list(\@listref, $maxlen, $field_sep);
3096
3097					Calls C<neat> on each element of the list and returns a string
3098					containing the results joined with C<$field_sep>. C<$field_sep> defaults
3099					to C<", ">.
3100
3101					=head3 C<looks_like_number>
3102
3103					@bool = looks_like_number(@array);
3104
3105					Returns true for each element that looks like a number.
3106					Returns false for each element that does not look like a number.
3107					Returns C<undef> for each element that is undefined or empty.
3108
3109					=head3 C<hash>
3110
3111					$hash_value = DBI::hash($buffer, $type);
3112
3113					Return a 32-bit integer 'hash' value corresponding to the contents of $buffer.
3114					The $type parameter selects which kind of hash algorithm should be used.
3115
3116					For the technically curious, type 0 (which is the default if $type
3117					isn't specified) is based on the Perl 5.1 hash except that the value
3118					is forced to be negative (for obscure historical reasons).
3119					Type 1 is the better "Fowler / Noll / Vo" (FNV) hash. See
3120					L<http://www.isthe.com/chongo/tech/comp/fnv/> for more information.
3121					Both types are implemented in C and are very fast.
3122
3123					This function doesn't have much to do with databases, except that
3124					it can be handy to store hash values in a database.
3125
3126					=head3 C<sql_type_cast>
3127
3128					$sts = DBI::sql_type_cast($sv, $sql_type, $flags);
3129
3130					sql_type_cast attempts to cast C<$sv> to the SQL type (see L<DBI
3131					Constants>) specified in C<$sql_type>. At present only the SQL types
3132					C<SQL_INTEGER>, C<SQL_DOUBLE> and C<SQL_NUMERIC> are supported.
3133
3134					For C<SQL_INTEGER> the effect is similar to using the value in an expression
3135					that requires an integer. It gives the perl scalar an 'integer aspect'.
3136					(Technically the value gains an IV, or possibly a UV or NV if the value is too
3137					large for an IV.)
3138
3139					For C<SQL_DOUBLE> the effect is similar to using the value in an expression
3140					that requires a general numeric value. It gives the perl scalar a 'numeric
3141					aspect'. (Technically the value gains an NV.)
3142
3143					C<SQL_NUMERIC> is similar to C<SQL_INTEGER> or C<SQL_DOUBLE> but more
3144					general and more cautious. It will look at the string first and if it
3145					looks like an integer (that will fit in an IV or UV) it will act like
3146					C<SQL_INTEGER>, if it looks like a floating point value it will act
3147					like C<SQL_DOUBLE>, if it looks like neither then it will do nothing -
3148					and thereby avoid the warnings that would be generated by
3149					C<SQL_INTEGER> and C<SQL_DOUBLE> when given non-numeric data.
3150
3151					C<$flags> may be:
3152
3153					=over 4
3154
3155					=item C<DBIstcf_DISCARD_STRING>
3156
3157					If this flag is specified then when the driver successfully casts the
3158					bound perl scalar to a non-string type then the string portion of the
3159					scalar will be discarded.
3160
3161					=item C<DBIstcf_STRICT>
3162
3163					If C<$sv> cannot be cast to the requested C<$sql_type> then by default
3164					it is left untouched and no error is generated. If you specify
3165					C<DBIstcf_STRICT> and the cast fails, this will generate an error.
3166
3167					=back
3168
3169					The returned C<$sts> value is:
3170
3171					-2 sql_type is not handled
3172					-1 sv is undef so unchanged
3173					0 sv could not be cast cleanly and DBIstcf_STRICT was used
3174					1 sv could not be cast and DBIstcf_STRICT was not used
3175					2 sv was cast successfully
3176
3177					This method is exported by the :utils tag and was introduced in DBI
3178					1.611.
3179
3180					=head2 DBI Dynamic Attributes
3181
3182					Dynamic attributes are always associated with the I<last handle used>
3183					(that handle is represented by C<$h> in the descriptions below).
3184
3185					Where an attribute is equivalent to a method call, then refer to
3186					the method call for all related documentation.
3187
3188					Warning: these attributes are provided as a convenience but they
3189					do have limitations. Specifically, they have a short lifespan:
3190					because they are associated with
3191					the last handle used, they should only be used I<immediately> after
3192					calling the method that "sets" them.
3193					If in any doubt, use the corresponding method call.
3194
3195					=head3 C<$DBI::err>
3196
3197					Equivalent to C<$h-E<gt>err>.
3198
3199					=head3 C<$DBI::errstr>
3200
3201					Equivalent to C<$h-E<gt>errstr>.
3202
3203					=head3 C<$DBI::state>
3204
3205					Equivalent to C<$h-E<gt>state>.
3206
3207					=head3 C<$DBI::rows>
3208
3209					Equivalent to C<$h-E<gt>rows>. Please refer to the documentation
3210					for the L</rows> method.
3211
3212					=head3 C<$DBI::lasth>
3213
3214					Returns the DBI object handle used for the most recent DBI method call.
3215					If the last DBI method call was a DESTROY then $DBI::lasth will return
3216					the handle of the parent of the destroyed handle, if there is one.
3217
3218
3219					=head1 METHODS COMMON TO ALL HANDLES
3220
3221					The following methods can be used by all types of DBI handles.
3222
3223					=head3 C<err>
3224
3225					$rv = $h->err;
3226
3227					Returns the I<native> database engine error code from the last driver
3228					method called. The code is typically an integer but you should not
3229					assume that.
3230
3231					The DBI resets $h->err to undef before almost all DBI method calls, so the
3232					value only has a short lifespan. Also, for most drivers, the statement
3233					handles share the same error variable as the parent database handle,
3234					so calling a method on one handle may reset the error on the
3235					related handles.
3236
3237					(Methods which don't reset err before being called include err() and errstr(),
3238					obviously, state(), rows(), func(), trace(), trace_msg(), ping(), and the
3239					tied hash attribute FETCH() and STORE() methods.)
3240
3241					If you need to test for specific error conditions I<and> have your program be
3242					portable to different database engines, then you'll need to determine what the
3243					corresponding error codes are for all those engines and test for all of them.
3244
3245					The DBI uses the value of $DBI::stderr as the C<err> value for internal errors.
3246					Drivers should also do likewise. The default value for $DBI::stderr is 2000000000.
3247
3248					A driver may return C<0> from err() to indicate a warning condition
3249					after a method call. Similarly, a driver may return an empty string
3250					to indicate a 'success with information' condition. In both these
3251					cases the value is false but not undef. The errstr() and state()
3252					methods may be used to retrieve extra information in these cases.
3253
3254					See L</set_err> for more information.
3255
3256					=head3 C<errstr>
3257
3258					$str = $h->errstr;
3259
3260					Returns the native database engine error message from the last DBI
3261					method called. This has the same lifespan issues as the L</err> method
3262					described above.
3263
3264					The returned string may contain multiple messages separated by
3265					newline characters.
3266
3267					The errstr() method should not be used to test for errors, use err()
3268					for that, because drivers may return 'success with information' or
3269					warning messages via errstr() for methods that have not 'failed'.
3270
3271					See L</set_err> for more information.
3272
3273					=head3 C<state>
3274
3275					$str = $h->state;
3276
3277					Returns a state code in the standard SQLSTATE five character format.
3278					Note that the specific success code C<00000> is translated to any empty string
3279					(false). If the driver does not support SQLSTATE (and most don't),
3280					then state() will return C<S1000> (General Error) for all errors.
3281
3282					The driver is free to return any value via C<state>, e.g., warning
3283					codes, even if it has not declared an error by returning a true value
3284					via the L</err> method described above.
3285
3286					The state() method should not be used to test for errors, use err()
3287					for that, because drivers may return a 'success with information' or
3288					warning state code via state() for methods that have not 'failed'.
3289
3290					=head3 C<set_err>
3291
3292					$rv = $h->set_err($err, $errstr);
3293					$rv = $h->set_err($err, $errstr, $state);
3294					$rv = $h->set_err($err, $errstr, $state, $method);
3295					$rv = $h->set_err($err, $errstr, $state, $method, $rv);
3296
3297					Set the C<err>, C<errstr>, and C<state> values for the handle.
3298					This method is typically only used by DBI drivers and DBI subclasses.
3299
3300					If the L</HandleSetErr> attribute holds a reference to a subroutine
3301					it is called first. The subroutine can alter the $err, $errstr, $state,
3302					and $method values. See L</HandleSetErr> for full details.
3303					If the subroutine returns a true value then the handle C<err>,
3304					C<errstr>, and C<state> values are not altered and set_err() returns
3305					an empty list (it normally returns $rv which defaults to undef, see below).
3306
3307					Setting C<err> to a I<true> value indicates an error and will trigger
3308					the normal DBI error handling mechanisms, such as C<RaiseError> and
3309					C<HandleError>, if they are enabled, when execution returns from
3310					the DBI back to the application.
3311
3312					Setting C<err> to C<""> indicates an 'information' state, and setting
3313					it to C<"0"> indicates a 'warning' state. Setting C<err> to C<undef>
3314					also sets C<errstr> to undef, and C<state> to C<"">, irrespective
3315					of the values of the $errstr and $state parameters.
3316
3317					The $method parameter provides an alternate method name for the
3318					C<RaiseError>/C<PrintError>/C<PrintWarn> error string instead of
3319					the fairly unhelpful 'C<set_err>'.
3320
3321					The C<set_err> method normally returns undef. The $rv parameter
3322					provides an alternate return value.
3323
3324					Some special rules apply if the C<err> or C<errstr>
3325					values for the handle are I<already> set...
3326
3327					If C<errstr> is true then: "C< [err was %s now %s]>" is appended if $err is
3328					true and C<err> is already true and the new err value differs from the original
3329					one. Similarly "C< [state was %s now %s]>" is appended if $state is true and C<state> is
3330					already true and the new state value differs from the original one. Finally
3331					"C<\n>" and the new $errstr are appended if $errstr differs from the existing
3332					errstr value. Obviously the C<%s>'s above are replaced by the corresponding values.
3333
3334					The handle C<err> value is set to $err if: $err is true; or handle
3335					C<err> value is undef; or $err is defined and the length is greater
3336					than the handle C<err> length. The effect is that an 'information'
3337					state only overrides undef; a 'warning' overrides undef or 'information',
3338					and an 'error' state overrides anything.
3339
3340					The handle C<state> value is set to $state if $state is true and
3341					the handle C<err> value was set (by the rules above).
3342
3343					Support for warning and information states was added in DBI 1.41.
3344
3345					=head3 C<trace>
3346
3347					$h->trace($trace_settings);
3348					$h->trace($trace_settings, $trace_filename);
3349					$trace_settings = $h->trace;
3350
3351					The trace() method is used to alter the trace settings for a handle
3352					(and any future children of that handle). It can also be used to
3353					change where the trace output is sent.
3354
3355					There's a similar method, C<DBI-E<gt>trace>, which sets the global
3356					default trace settings.
3357
3358					See the L</TRACING> section for full details about the DBI's powerful
3359					tracing facilities.
3360
3361					=head3 C<trace_msg>
3362
3363					$h->trace_msg($message_text);
3364					$h->trace_msg($message_text, $min_level);
3365
3366					Writes C<$message_text> to the trace file if the trace level is
3367					greater than or equal to $min_level (which defaults to 1).
3368					Can also be called as C<DBI-E<gt>trace_msg($msg)>.
3369
3370					See L</TRACING> for more details.
3371
3372					=head3 C<func>
3373
3374					$h->func(@func_arguments, $func_name) or die ...;
3375
3376					The C<func> method can be used to call private non-standard and
3377					non-portable methods implemented by the driver. Note that the function
3378					name is given as the I<last> argument.
3379
3380					It's also important to note that the func() method does not clear
3381					a previous error ($DBI::err etc.) and it does not trigger automatic
3382					error detection (RaiseError etc.) so you must check the return
3383					status and/or $h->err to detect errors.
3384
3385					(This method is not directly related to calling stored procedures.
3386					Calling stored procedures is currently not defined by the DBI.
3387					Some drivers, such as DBD::Oracle, support it in non-portable ways.
3388					See driver documentation for more details.)
3389
3390					See also install_method() in L<DBI::DBD> for how you can avoid needing to
3391					use func() and gain direct access to driver-private methods.
3392
3393					=head3 C<can>
3394
3395					$is_implemented = $h->can($method_name);
3396
3397					Returns true if $method_name is implemented by the driver or a
3398					default method is provided by the DBI's driver base class.
3399					It returns false where a driver hasn't implemented a method and the
3400					default method is provided by the DBI's driver base class is just an empty stub.
3401
3402					=head3 C<parse_trace_flags>
3403
3404					$trace_settings_integer = $h->parse_trace_flags($trace_settings);
3405
3406					Parses a string containing trace settings and returns the corresponding
3407					integer value used internally by the DBI and drivers.
3408
3409					The $trace_settings argument is a string containing a trace level
3410					between 0 and 15 and/or trace flag names separated by vertical bar
3411					("C<\|>") or comma ("C<,>") characters. For example: C<"SQL\|3\|foo">.
3412
3413					It uses the parse_trace_flag() method, described below, to process
3414					the individual trace flag names.
3415
3416					The parse_trace_flags() method was added in DBI 1.42.
3417
3418					=head3 C<parse_trace_flag>
3419
3420					$bit_flag = $h->parse_trace_flag($trace_flag_name);
3421
3422					Returns the bit flag corresponding to the trace flag name in
3423					$trace_flag_name. Drivers are expected to override this method and
3424					check if $trace_flag_name is a driver specific trace flags and, if
3425					not, then call the DBI's default parse_trace_flag().
3426
3427					The parse_trace_flag() method was added in DBI 1.42.
3428
3429					=head3 C<private_attribute_info>
3430
3431					$hash_ref = $h->private_attribute_info();
3432
3433					Returns a reference to a hash whose keys are the names of driver-private
3434					handle attributes available for the kind of handle (driver, database, statement)
3435					that the method was called on.
3436
3437					For example, the return value when called with a DBD::Sybase $dbh could look like this:
3438
3439					{
3440					syb_dynamic_supported => undef,
3441					syb_oc_version => undef,
3442					syb_server_version => undef,
3443					syb_server_version_string => undef,
3444					}
3445
3446					and when called with a DBD::Sybase $sth they could look like this:
3447
3448					{
3449					syb_types => undef,
3450					syb_proc_status => undef,
3451					syb_result_type => undef,
3452					}
3453
3454					The values should be undef. Meanings may be assigned to particular values in future.
3455
3456					=head3 C<swap_inner_handle>
3457
3458					$rc = $h1->swap_inner_handle( $h2 );
3459					$rc = $h1->swap_inner_handle( $h2, $allow_reparent );
3460
3461					Brain transplants for handles. You don't need to know about this
3462					unless you want to become a handle surgeon.
3463
3464					A DBI handle is a reference to a tied hash. A tied hash has an
3465					I<inner> hash that actually holds the contents. The swap_inner_handle()
3466					method swaps the inner hashes between two handles. The $h1 and $h2
3467					handles still point to the same tied hashes, but what those hashes
3468					are tied to has been swapped. In effect $h1 I<becomes> $h2 and
3469					vice-versa. This is powerful stuff, expect problems. Use with care.
3470
3471					As a small safety measure, the two handles, $h1 and $h2, have to
3472					share the same parent unless $allow_reparent is true.
3473
3474					The swap_inner_handle() method was added in DBI 1.44.
3475
3476					Here's a quick kind of 'diagram' as a worked example to help think about what's
3477					happening:
3478
3479					Original state:
3480					dbh1o -> dbh1i
3481					sthAo -> sthAi(dbh1i)
3482					dbh2o -> dbh2i
3483
3484					swap_inner_handle dbh1o with dbh2o:
3485					dbh2o -> dbh1i
3486					sthAo -> sthAi(dbh1i)
3487					dbh1o -> dbh2i
3488
3489					create new sth from dbh1o:
3490					dbh2o -> dbh1i
3491					sthAo -> sthAi(dbh1i)
3492					dbh1o -> dbh2i
3493					sthBo -> sthBi(dbh2i)
3494
3495					swap_inner_handle sthAo with sthBo:
3496					dbh2o -> dbh1i
3497					sthBo -> sthAi(dbh1i)
3498					dbh1o -> dbh2i
3499					sthAo -> sthBi(dbh2i)
3500
3501					=head3 C<visit_child_handles>
3502
3503					$h->visit_child_handles( $coderef );
3504					$h->visit_child_handles( $coderef, $info );
3505
3506					Where $coderef is a reference to a subroutine and $info is an arbitrary value
3507					which, if undefined, defaults to a reference to an empty hash. Returns $info.
3508
3509					For each child handle of $h, if any, $coderef is invoked as:
3510
3511					$coderef->($child_handle, $info);
3512
3513					If the execution of $coderef returns a true value then C<visit_child_handles>
3514					is called on that child handle and passed the returned value as $info.
3515
3516					For example:
3517
3518					# count database connections with names (DSN) matching a pattern
3519					my $connections = 0;
3520					$dbh->{Driver}->visit_child_handles(sub {
3521					my ($h, $info) = @_;
3522					++$connections if $h->{Name} =~ /foo/;
3523					return 0; # don't visit kids
3524					})
3525
3526					See also L</visit_handles>.
3527
3528					=head1 ATTRIBUTES COMMON TO ALL HANDLES
3529
3530					These attributes are common to all types of DBI handles.
3531
3532					Some attributes are inherited by child handles. That is, the value
3533					of an inherited attribute in a newly created statement handle is the
3534					same as the value in the parent database handle. Changes to attributes
3535					in the new statement handle do not affect the parent database handle
3536					and changes to the database handle do not affect existing statement
3537					handles, only future ones.
3538
3539					Attempting to set or get the value of an unknown attribute generates a warning,
3540					except for private driver specific attributes (which all have names
3541					starting with a lowercase letter).
3542
3543					Example:
3544
3545					$h->{AttributeName} = ...; # set/write
3546					... = $h->{AttributeName}; # get/read
3547
3548					=head3 C<Warn>
3549
3550					Type: boolean, inherited
3551
3552					The C<Warn> attribute enables useful warnings for certain bad
3553					practices. It is enabled by default and should only be disabled in
3554					rare circumstances. Since warnings are generated using the Perl
3555					C<warn> function, they can be intercepted using the Perl C<$SIG{__WARN__}>
3556					hook.
3557
3558					The C<Warn> attribute is not related to the C<PrintWarn> attribute.
3559
3560					=head3 C<Active>
3561
3562					Type: boolean, read-only
3563
3564					The C<Active> attribute is true if the handle object is "active". This is rarely used in
3565					applications. The exact meaning of active is somewhat vague at the
3566					moment. For a database handle it typically means that the handle is
3567					connected to a database (C<$dbh-E<gt>disconnect> sets C<Active> off). For
3568					a statement handle it typically means that the handle is a C<SELECT>
3569					that may have more data to fetch. (Fetching all the data or calling C<$sth-E<gt>finish>
3570					sets C<Active> off.)
3571
3572					=head3 C<Executed>
3573
3574					Type: boolean
3575
3576					The C<Executed> attribute is true if the handle object has been "executed".
3577					Currently only the $dbh do() method and the $sth execute(), execute_array(),
3578					and execute_for_fetch() methods set the C<Executed> attribute.
3579
3580					When it's set on a handle it is also set on the parent handle at the
3581					same time. So calling execute() on a $sth also sets the C<Executed>
3582					attribute on the parent $dbh.
3583
3584					The C<Executed> attribute for a database handle is cleared by the commit() and
3585					rollback() methods (even if they fail). The C<Executed> attribute of a
3586					statement handle is not cleared by the DBI under any circumstances and so acts
3587					as a permanent record of whether the statement handle was ever used.
3588
3589					The C<Executed> attribute was added in DBI 1.41.
3590
3591					=head3 C<Kids>
3592
3593					Type: integer, read-only
3594
3595					For a driver handle, C<Kids> is the number of currently existing database
3596					handles that were created from that driver handle. For a database
3597					handle, C<Kids> is the number of currently existing statement handles that
3598					were created from that database handle.
3599					For a statement handle, the value is zero.
3600
3601					=head3 C<ActiveKids>
3602
3603					Type: integer, read-only
3604
3605					Like C<Kids>, but only counting those that are C<Active> (as above).
3606
3607					=head3 C<CachedKids>
3608
3609					Type: hash ref
3610
3611					For a database handle, C<CachedKids> returns a reference to the cache (hash) of
3612					statement handles created by the L</prepare_cached> method. For a
3613					driver handle, returns a reference to the cache (hash) of
3614					database handles created by the L</connect_cached> method.
3615
3616					=head3 C<Type>
3617
3618					Type: scalar, read-only
3619
3620					The C<Type> attribute identifies the type of a DBI handle. Returns
3621					"dr" for driver handles, "db" for database handles and "st" for
3622					statement handles.
3623
3624					=head3 C<ChildHandles>
3625
3626					Type: array ref
3627
3628					The ChildHandles attribute contains a reference to an array of all the
3629					handles created by this handle which are still accessible. The
3630					contents of the array are weak-refs and will become undef when the
3631					handle goes out of scope.
3632
3633					C<ChildHandles> returns undef if your perl version does not support weak
3634					references (check the L<Scalar::Util\|Scalar::Util> module). The referenced
3635					array returned should be treated as read-only.
3636
3637					For example, to enumerate all driver handles, database handles and
3638					statement handles:
3639
3640					sub show_child_handles {
3641					my ($h, $level) = @_;
3642					printf "%sh %s %s\n", $h->{Type}, "\t" x $level, $h;
3643					show_child_handles($_, $level + 1)
3644					for (grep { defined } @{$h->{ChildHandles}});
3645					}
3646
3647					my %drivers = DBI->installed_drivers();
3648					show_child_handles($_, 0) for (values %drivers);
3649
3650					=head3 C<CompatMode>
3651
3652					Type: boolean, inherited
3653
3654					The C<CompatMode> attribute is used by emulation layers (such as
3655					Oraperl) to enable compatible behaviour in the underlying driver
3656					(e.g., DBD::Oracle) for this handle. Not normally set by application code.
3657
3658					It also has the effect of disabling the 'quick FETCH' of attribute
3659					values from the handles attribute cache. So all attribute values
3660					are handled by the drivers own FETCH method. This makes them slightly
3661					slower but is useful for special-purpose drivers like DBD::Multiplex.
3662
3663					=head3 C<InactiveDestroy>
3664
3665					Type: boolean
3666
3667					The default value, false, means a handle will be fully destroyed
3668					as normal when the last reference to it is removed, just as you'd expect.
3669
3670					If set true then the handle will be treated by the DESTROY as if it was no
3671					longer Active, and so the I<database engine> related effects of DESTROYing a
3672					handle will be skipped. Think of the name as meaning 'treat the handle as
3673					not-Active in the DESTROY method'.
3674
3675					For a database handle, this attribute does not disable an I<explicit>
3676					call to the disconnect method, only the implicit call from DESTROY
3677					that happens if the handle is still marked as C<Active>.
3678
3679					This attribute is specifically designed for use in Unix applications
3680					that "fork" child processes. For some drivers, when the child process exits
3681					the destruction of inherited handles cause the corresponding handles in the
3682					parent process to cease working.
3683
3684					Either the parent or the child process, but not both, should set
3685					C<InactiveDestroy> true on all their shared handles. Alternatively the
3686					L</AutoInactiveDestroy> can be set in the parent on connect.
3687
3688					To help tracing applications using fork the process id is shown in
3689					the trace log whenever a DBI or handle trace() method is called.
3690					The process id also shown for I<every> method call if the DBI trace
3691					level (not handle trace level) is set high enough to show the trace
3692					from the DBI's method dispatcher, e.g. >= 9.
3693
3694					=head3 C<AutoInactiveDestroy>
3695
3696					Type: boolean, inherited
3697
3698					The L</InactiveDestroy> attribute, described above, needs to be explicitly set
3699					in the child process after a fork(). This is a problem if the code that performs
3700					the fork() is not under your control, perhaps in a third-party module.
3701					Use C<AutoInactiveDestroy> to get around this situation.
3702
3703					If set true, the DESTROY method will check the process id of the handle and, if
3704					different from the current process id, it will set the I<InactiveDestroy> attribute.
3705
3706					This is the example it's designed to deal with:
3707
3708					my $dbh = DBI->connect(...);
3709					some_code_that_forks(); # Perhaps without your knowledge
3710					# Child process dies, destroying the inherited dbh
3711					$dbh->do(...); # Breaks because parent $dbh is now broken
3712
3713					The C<AutoInactiveDestroy> attribute was added in DBI 1.614.
3714
3715					=head3 C<PrintWarn>
3716
3717					Type: boolean, inherited
3718
3719					The C<PrintWarn> attribute controls the printing of warnings recorded
3720					by the driver. When set to a true value (the default) the DBI will check method
3721					calls to see if a warning condition has been set. If so, the DBI
3722					will effectively do a C<warn("$class $method warning: $DBI::errstr")>
3723					where C<$class> is the driver class and C<$method> is the name of
3724					the method which failed. E.g.,
3725
3726					DBD::Oracle::db execute warning: ... warning text here ...
3727
3728					If desired, the warnings can be caught and processed using a C<$SIG{__WARN__}>
3729					handler or modules like CGI::Carp and CGI::ErrorWrap.
3730
3731					See also L</set_err> for how warnings are recorded and L</HandleSetErr>
3732					for how to influence it.
3733
3734					Fetching the full details of warnings can require an extra round-trip
3735					to the database server for some drivers. In which case the driver
3736					may opt to only fetch the full details of warnings if the C<PrintWarn>
3737					attribute is true. If C<PrintWarn> is false then these drivers should
3738					still indicate the fact that there were warnings by setting the
3739					warning string to, for example: "3 warnings".
3740
3741					=head3 C<PrintError>
3742
3743					Type: boolean, inherited
3744
3745					The C<PrintError> attribute can be used to force errors to generate warnings (using
3746					C<warn>) in addition to returning error codes in the normal way. When set
3747					"on", any method which results in an error occurring will cause the DBI to
3748					effectively do a C<warn("$class $method failed: $DBI::errstr")> where C<$class>
3749					is the driver class and C<$method> is the name of the method which failed. E.g.,
3750
3751					DBD::Oracle::db prepare failed: ... error text here ...
3752
3753					By default, C<DBI-E<gt>connect> sets C<PrintError> "on".
3754
3755					If desired, the warnings can be caught and processed using a C<$SIG{__WARN__}>
3756					handler or modules like CGI::Carp and CGI::ErrorWrap.
3757
3758					=head3 C<RaiseError>
3759
3760					Type: boolean, inherited
3761
3762					The C<RaiseError> attribute can be used to force errors to raise exceptions rather
3763					than simply return error codes in the normal way. It is "off" by default.
3764					When set "on", any method which results in an error will cause
3765					the DBI to effectively do a C<die("$class $method failed: $DBI::errstr")>,
3766					where C<$class> is the driver class and C<$method> is the name of the method
3767					that failed. E.g.,
3768
3769					DBD::Oracle::db prepare failed: ... error text here ...
3770
3771					If you turn C<RaiseError> on then you'd normally turn C<PrintError> off.
3772					If C<PrintError> is also on, then the C<PrintError> is done first (naturally).
3773
3774					Typically C<RaiseError> is used in conjunction with C<eval { ... }>
3775					to catch the exception that's been thrown and followed by an
3776					C<if ($@) { ... }> block to handle the caught exception.
3777					For example:
3778
3779					eval {
3780					...
3781					$sth->execute();
3782					...
3783					};
3784					if ($@) {
3785					# $sth->err and $DBI::err will be true if error was from DBI
3786					warn $@; # print the error
3787					... # do whatever you need to deal with the error
3788					}
3789
3790					In that eval block the $DBI::lasth variable can be useful for
3791					diagnosis and reporting if you can't be sure which handle triggered
3792					the error. For example, $DBI::lasth->{Type} and $DBI::lasth->{Statement}.
3793
3794					See also L</Transactions>.
3795
3796					If you want to temporarily turn C<RaiseError> off (inside a library function
3797					that is likely to fail, for example), the recommended way is like this:
3798
3799					{
3800					local $h->{RaiseError}; # localize and turn off for this block
3801					...
3802					}
3803
3804					The original value will automatically and reliably be restored by Perl,
3805					regardless of how the block is exited.
3806					The same logic applies to other attributes, including C<PrintError>.
3807
3808					=head3 C<HandleError>
3809
3810					Type: code ref, inherited
3811
3812					The C<HandleError> attribute can be used to provide your own alternative behaviour
3813					in case of errors. If set to a reference to a subroutine then that
3814					subroutine is called when an error is detected (at the same point that
3815					C<RaiseError> and C<PrintError> are handled).
3816
3817					The subroutine is called with three parameters: the error message
3818					string that C<RaiseError> and C<PrintError> would use,
3819					the DBI handle being used, and the first value being returned by
3820					the method that failed (typically undef).
3821
3822					If the subroutine returns a false value then the C<RaiseError>
3823					and/or C<PrintError> attributes are checked and acted upon as normal.
3824
3825					For example, to C<die> with a full stack trace for any error:
3826
3827					use Carp;
3828					$h->{HandleError} = sub { confess(shift) };
3829
3830					Or to turn errors into exceptions:
3831
3832					use Exception; # or your own favourite exception module
3833					$h->{HandleError} = sub { Exception->new('DBI')->raise($_[0]) };
3834
3835					It is possible to 'stack' multiple HandleError handlers by using
3836					closures:
3837
3838					sub your_subroutine {
3839					my $previous_handler = $h->{HandleError};
3840					$h->{HandleError} = sub {
3841					return 1 if $previous_handler and &$previous_handler(@_);
3842					... your code here ...
3843					};
3844					}
3845
3846					Using a C<my> inside a subroutine to store the previous C<HandleError>
3847					value is important. See L<perlsub> and L<perlref> for more information
3848					about I<closures>.
3849
3850					It is possible for C<HandleError> to alter the error message that
3851					will be used by C<RaiseError> and C<PrintError> if it returns false.
3852					It can do that by altering the value of $_[0]. This example appends
3853					a stack trace to all errors and, unlike the previous example using
3854					Carp::confess, this will work C<PrintError> as well as C<RaiseError>:
3855
3856					$h->{HandleError} = sub { $_[0]=Carp::longmess($_[0]); 0; };
3857
3858					It is also possible for C<HandleError> to hide an error, to a limited
3859					degree, by using L</set_err> to reset $DBI::err and $DBI::errstr,
3860					and altering the return value of the failed method. For example:
3861
3862					$h->{HandleError} = sub {
3863					return 0 unless $_[0] =~ /^\S+ fetchrow_arrayref failed:/;
3864					return 0 unless $_[1]->err == 1234; # the error to 'hide'
3865					$h->set_err(undef,undef); # turn off the error
3866					$_[2] = [ ... ]; # supply alternative return value
3867					return 1;
3868					};
3869
3870					This only works for methods which return a single value and is hard
3871					to make reliable (avoiding infinite loops, for example) and so isn't
3872					recommended for general use! If you find a I<good> use for it then
3873					please let me know.
3874
3875					=head3 C<HandleSetErr>
3876
3877					Type: code ref, inherited
3878
3879					The C<HandleSetErr> attribute can be used to intercept
3880					the setting of handle C<err>, C<errstr>, and C<state> values.
3881					If set to a reference to a subroutine then that subroutine is called
3882					whenever set_err() is called, typically by the driver or a subclass.
3883
3884					The subroutine is called with five arguments, the first five that
3885					were passed to set_err(): the handle, the C<err>, C<errstr>, and
3886					C<state> values being set, and the method name. These can be altered
3887					by changing the values in the @_ array. The return value affects
3888					set_err() behaviour, see L</set_err> for details.
3889
3890					It is possible to 'stack' multiple HandleSetErr handlers by using
3891					closures. See L</HandleError> for an example.
3892
3893					The C<HandleSetErr> and C<HandleError> subroutines differ in subtle
3894					but significant ways. HandleError is only invoked at the point where
3895					the DBI is about to return to the application with C<err> set true.
3896					It's not invoked by the failure of a method that's been called by
3897					another DBI method. HandleSetErr, on the other hand, is called
3898					whenever set_err() is called with a defined C<err> value, even if false.
3899					So it's not just for errors, despite the name, but also warn and info states.
3900					The set_err() method, and thus HandleSetErr, may be called multiple
3901					times within a method and is usually invoked from deep within driver code.
3902
3903					In theory a driver can use the return value from HandleSetErr via
3904					set_err() to decide whether to continue or not. If set_err() returns
3905					an empty list, indicating that the HandleSetErr code has 'handled'
3906					the 'error', the driver could then continue instead of failing (if
3907					that's a reasonable thing to do). This isn't excepted to be
3908					common and any such cases should be clearly marked in the driver
3909					documentation and discussed on the dbi-dev mailing list.
3910
3911					The C<HandleSetErr> attribute was added in DBI 1.41.
3912
3913					=head3 C<ErrCount>
3914
3915					Type: unsigned integer
3916
3917					The C<ErrCount> attribute is incremented whenever the set_err()
3918					method records an error. It isn't incremented by warnings or
3919					information states. It is not reset by the DBI at any time.
3920
3921					The C<ErrCount> attribute was added in DBI 1.41. Older drivers may
3922					not have been updated to use set_err() to record errors and so this
3923					attribute may not be incremented when using them.
3924
3925
3926					=head3 C<ShowErrorStatement>
3927
3928					Type: boolean, inherited
3929
3930					The C<ShowErrorStatement> attribute can be used to cause the relevant
3931					Statement text to be appended to the error messages generated by
3932					the C<RaiseError>, C<PrintError>, and C<PrintWarn> attributes.
3933					Only applies to errors on statement handles
3934					plus the prepare(), do(), and the various C<select*()> database handle methods.
3935					(The exact format of the appended text is subject to change.)
3936
3937					If C<$h-E<gt>{ParamValues}> returns a hash reference of parameter
3938					(placeholder) values then those are formatted and appended to the
3939					end of the Statement text in the error message.
3940
3941					=head3 C<TraceLevel>
3942
3943					Type: integer, inherited
3944
3945					The C<TraceLevel> attribute can be used as an alternative to the
3946					L</trace> method to set the DBI trace level and trace flags for a
3947					specific handle. See L</TRACING> for more details.
3948
3949					The C<TraceLevel> attribute is especially useful combined with
3950					C<local> to alter the trace settings for just a single block of code.
3951
3952					=head3 C<FetchHashKeyName>
3953
3954					Type: string, inherited
3955
3956					The C<FetchHashKeyName> attribute is used to specify whether the fetchrow_hashref()
3957					method should perform case conversion on the field names used for
3958					the hash keys. For historical reasons it defaults to 'C<NAME>' but
3959					it is recommended to set it to 'C<NAME_lc>' (convert to lower case)
3960					or 'C<NAME_uc>' (convert to upper case) according to your preference.
3961					It can only be set for driver and database handles. For statement
3962					handles the value is frozen when prepare() is called.
3963
3964
3965					=head3 C<ChopBlanks>
3966
3967					Type: boolean, inherited
3968
3969					The C<ChopBlanks> attribute can be used to control the trimming of trailing space
3970					characters from fixed width character (CHAR) fields. No other field
3971					types are affected, even where field values have trailing spaces.
3972
3973					The default is false (although it is possible that the default may change).
3974					Applications that need specific behaviour should set the attribute as
3975					needed.
3976
3977					Drivers are not required to support this attribute, but any driver which
3978					does not support it must arrange to return C<undef> as the attribute value.
3979
3980
3981					=head3 C<LongReadLen>
3982
3983					Type: unsigned integer, inherited
3984
3985					The C<LongReadLen> attribute may be used to control the maximum
3986					length of 'long' type fields (LONG, BLOB, CLOB, MEMO, etc.) which the driver will
3987					read from the database automatically when it fetches each row of data.
3988
3989					The C<LongReadLen> attribute only relates to fetching and reading
3990					long values; it is not involved in inserting or updating them.
3991
3992					A value of 0 means not to automatically fetch any long data.
3993					Drivers may return undef or an empty string for long fields when
3994					C<LongReadLen> is 0.
3995
3996					The default is typically 0 (zero) or 80 bytes but may vary between drivers.
3997					Applications fetching long fields should set this value to slightly
3998					larger than the longest long field value to be fetched.
3999
4000					Some databases return some long types encoded as pairs of hex digits.
4001					For these types, C<LongReadLen> relates to the underlying data
4002					length and not the doubled-up length of the encoded string.
4003
4004					Changing the value of C<LongReadLen> for a statement handle after it
4005					has been C<prepare>'d will typically have no effect, so it's common to
4006					set C<LongReadLen> on the C<$dbh> before calling C<prepare>.
4007
4008					For most drivers the value used here has a direct effect on the
4009					memory used by the statement handle while it's active, so don't be
4010					too generous. If you can't be sure what value to use you could
4011					execute an extra select statement to determine the longest value.
4012					For example:
4013
4014					$dbh->{LongReadLen} = $dbh->selectrow_array(qq{
4015					SELECT MAX(OCTET_LENGTH(long_column_name))
4016					FROM table WHERE ...
4017					});
4018					$sth = $dbh->prepare(qq{
4019					SELECT long_column_name, ... FROM table WHERE ...
4020					});
4021
4022					You may need to take extra care if the table can be modified between
4023					the first select and the second being executed. You may also need to
4024					use a different function if OCTET_LENGTH() does not work for long
4025					types in your database. For example, for Sybase use DATALENGTH() and
4026					for Oracle use LENGTHB().
4027
4028					See also L</LongTruncOk> for information on truncation of long types.
4029
4030					=head3 C<LongTruncOk>
4031
4032					Type: boolean, inherited
4033
4034					The C<LongTruncOk> attribute may be used to control the effect of
4035					fetching a long field value which has been truncated (typically
4036					because it's longer than the value of the C<LongReadLen> attribute).
4037
4038					By default, C<LongTruncOk> is false and so fetching a long value that
4039					needs to be truncated will cause the fetch to fail.
4040					(Applications should always be sure to
4041					check for errors after a fetch loop in case an error, such as a divide
4042					by zero or long field truncation, caused the fetch to terminate
4043					prematurely.)
4044
4045					If a fetch fails due to a long field truncation when C<LongTruncOk> is
4046					false, many drivers will allow you to continue fetching further rows.
4047
4048					See also L</LongReadLen>.
4049
4050					=head3 C<TaintIn>
4051
4052					Type: boolean, inherited
4053
4054					If the C<TaintIn> attribute is set to a true value I<and> Perl is running in
4055					taint mode (e.g., started with the C<-T> option), then all the arguments
4056					to most DBI method calls are checked for being tainted. I<This may change.>
4057
4058					The attribute defaults to off, even if Perl is in taint mode.
4059					See L<perlsec> for more about taint mode. If Perl is not
4060					running in taint mode, this attribute has no effect.
4061
4062					When fetching data that you trust you can turn off the TaintIn attribute,
4063					for that statement handle, for the duration of the fetch loop.
4064
4065					The C<TaintIn> attribute was added in DBI 1.31.
4066
4067					=head3 C<TaintOut>
4068
4069					Type: boolean, inherited
4070
4071					If the C<TaintOut> attribute is set to a true value I<and> Perl is running in
4072					taint mode (e.g., started with the C<-T> option), then most data fetched
4073					from the database is considered tainted. I<This may change.>
4074
4075					The attribute defaults to off, even if Perl is in taint mode.
4076					See L<perlsec> for more about taint mode. If Perl is not
4077					running in taint mode, this attribute has no effect.
4078
4079					When fetching data that you trust you can turn off the TaintOut attribute,
4080					for that statement handle, for the duration of the fetch loop.
4081
4082					Currently only fetched data is tainted. It is possible that the results
4083					of other DBI method calls, and the value of fetched attributes, may
4084					also be tainted in future versions. That change may well break your
4085					applications unless you take great care now. If you use DBI Taint mode,
4086					please report your experience and any suggestions for changes.
4087
4088					The C<TaintOut> attribute was added in DBI 1.31.
4089
4090					=head3 C<Taint>
4091
4092					Type: boolean, inherited
4093
4094					The C<Taint> attribute is a shortcut for L</TaintIn> and L</TaintOut> (it is also present
4095					for backwards compatibility).
4096
4097					Setting this attribute sets both L</TaintIn> and L</TaintOut>, and retrieving
4098					it returns a true value if and only if L</TaintIn> and L</TaintOut> are
4099					both set to true values.
4100
4101					=head3 C<Profile>
4102
4103					Type: inherited
4104
4105					The C<Profile> attribute enables the collection and reporting of
4106					method call timing statistics. See the L<DBI::Profile> module
4107					documentation for I<much> more detail.
4108
4109					The C<Profile> attribute was added in DBI 1.24.
4110
4111					=head3 C<ReadOnly>
4112
4113					Type: boolean, inherited
4114
4115					An application can set the C<ReadOnly> attribute of a handle to a true value to
4116					indicate that it will not be attempting to make any changes using that handle
4117					or any children of it.
4118
4119					Note that the exact definition of 'read only' is rather fuzzy.
4120					For more details see the documentation for the driver you're using.
4121
4122					If the driver can make the handle truly read-only then it should
4123					(unless doing so would have unpleasant side effect, like changing the
4124					consistency level from per-statement to per-session).
4125					Otherwise the attribute is simply advisory.
4126
4127					A driver can set the C<ReadOnly> attribute itself to indicate that the data it
4128					is connected to cannot be changed for some reason.
4129
4130					If the driver cannot ensure the C<ReadOnly> attribute is adhered to it
4131					will record a warning. In this case reading the C<ReadOnly> attribute
4132					back after it is set true will return true even if the underlying
4133					driver cannot ensure this (so any application knows the application
4134					declared itself ReadOnly).
4135
4136					Library modules and proxy drivers can use the attribute to influence
4137					their behavior. For example, the DBD::Gofer driver considers the
4138					C<ReadOnly> attribute when making a decision about whether to retry an
4139					operation that failed.
4140
4141					The attribute should be set to 1 or 0 (or undef). Other values are reserved.
4142
4143					=head3 C<Callbacks>
4144
4145					Type: hash ref
4146
4147					The DBI callback mechanism lets you intercept, and optionally replace, any
4148					method call on a DBI handle. At the extreme, it lets you become a puppet
4149					master, deceiving the application in any way you want.
4150
4151					The C<Callbacks> attribute is a hash reference where the keys are DBI method
4152					names and the values are code references. For each key naming a method, the
4153					DBI will execute the associated code reference before executing the method.
4154
4155					The arguments to the code reference will be the same as to the method,
4156					including the invocant (a database handle or statement handle). For example,
4157					say that to callback to some code on a call to C<prepare()>:
4158
4159					$dbh->{Callbacks} = {
4160					prepare => sub {
4161					my ($dbh, $query, $attrs) = @_;
4162					print "Preparing q{$query}\n"
4163					},
4164					};
4165
4166					The callback would then be executed when you called the C<prepare()> method:
4167
4168					$dbh->prepare('SELECT 1');
4169
4170					And the output of course would be:
4171
4172					Preparing q{SELECT 1}
4173
4174					Because callbacks are executed I<before> the methods
4175					they're associated with, you can modify the arguments before they're passed on
4176					to the method call. For example, to make sure that all calls to C<prepare()>
4177					are immediately prepared by L<DBD::Pg>, add a callback that makes sure that
4178					the C<pg_prepare_now> attribute is always set:
4179
4180					my $dbh = DBI->connect($dsn, $username, $auth, {
4181					Callbacks => {
4182					prepare => sub {
4183					$_[2] \|\|= {};
4184					$_[2]->{pg_prepare_now} = 1;
4185					return; # must return nothing
4186					},
4187					}
4188					});
4189
4190					Note that we are editing the contents of C<@_> directly. In this case we've
4191					created the attributes hash if it's not passed to the C<prepare> call.
4192
4193					You can also prevent the associated method from ever executing. While a
4194					callback executes, C<$_> holds the method name. (This allows multiple callbacks
4195					to share the same code reference and still know what method was called.)
4196					To prevent the method from
4197					executing, simply C<undef $_>. For example, if you wanted to disable calls to
4198					C<ping()>, you could do this:
4199
4200					$dbh->{Callbacks} = {
4201					ping => sub {
4202					# tell dispatch to not call the method:
4203					undef $_;
4204					# return this value instead:
4205					return "42 bells";
4206					}
4207					};
4208
4209					As with other attributes, Callbacks can be specified on a handle or via the
4210					attributes to C<connect()>. Callbacks can also be applied to a statement
4211					methods on a statement handle. For example:
4212
4213					$sth->{Callbacks} = {
4214					execute => sub {
4215					print "Executing ", shift->{Statement}, "\n";
4216					}
4217					};
4218
4219					The C<Callbacks> attribute of a database handle isn't copied to any statement
4220					handles it creates. So setting callbacks for a statement handle requires you to
4221					set the C<Callbacks> attribute on the statement handle yourself, as in the
4222					example above, or use the special C<ChildCallbacks> key described below.
4223
4224					B<Special Keys in Callbacks Attribute>
4225
4226					In addition to DBI handle method names, the C<Callbacks> hash reference
4227					supports four additional keys.
4228
4229					The first is the C<ChildCallbacks> key. When a statement handle is created from
4230					a database handle the C<ChildCallbacks> key of the database handle's
4231					C<Callbacks> attribute, if any, becomes the new C<Callbacks> attribute of the
4232					statement handle.
4233					This allows you to define callbacks for all statement handles created from a
4234					database handle. For example, if you wanted to count how many times C<execute>
4235					was called in your application, you could write:
4236
4237					my $exec_count = 0;
4238					my $dbh = DBI->connect( $dsn, $username, $auth, {
4239					Callbacks => {
4240					ChildCallbacks => {
4241					execute => sub { $exec_count++; return; }
4242					}
4243					}
4244					});
4245
4246					END {
4247					print "The execute method was called $exec_count times\n";
4248					}
4249
4250					The other three special keys are C<connect_cached.new>,
4251					C<connect_cached.connected>, and C<connect_cached.reused>. These keys define
4252					callbacks that are called when C<connect_cached()> is called, but allow
4253					different behaviors depending on whether a new handle is created or a handle
4254					is returned. The callback is invoked with these arguments:
4255					C<$dbh, $dsn, $user, $auth, $attr>.
4256
4257					For example, some applications uses C<connect_cached()> to connect with
4258					C<AutoCommit> enabled and then disable C<AutoCommit> temporarily for
4259					transactions. If C<connect_cached()> is called during a transaction, perhaps in
4260					a utility method, then it might select the same cached handle and then force
4261					C<AutoCommit> on, forcing a commit of the transaction. See the L</connect_cached>
4262					documentation for one way to deal with that. Here we'll describe an alternative
4263					approach using a callback.
4264
4265					Because the C<connect_cached.new> and C<connect_cached.reused> callbacks are
4266					invoked before C<connect_cached()> has applied the connect attributes, you can
4267					use them to edit the attributes that will be applied. To prevent a cached
4268					handle from having its transactions committed before it's returned, you can
4269					eliminate the C<AutoCommit> attribute in a C<connect_cached.reused> callback,
4270					like so:
4271
4272					my $cb = {
4273					'connect_cached.reused' => sub { delete $_[4]->{AutoCommit} },
4274					};
4275
4276					sub dbh {
4277					my $self = shift;
4278					DBI->connect_cached( $dsn, $username, $auth, {
4279					PrintError => 0,
4280					RaiseError => 1,
4281					AutoCommit => 1,
4282					Callbacks => $cb,
4283					});
4284					}
4285
4286					The upshot is that new database handles are created with C<AutoCommit>
4287					enabled, while cached database handles are left in whatever transaction state
4288					they happened to be in when retrieved from the cache.
4289
4290					Note that we've also used a lexical for the callbacks hash reference. This is
4291					because C<connect_cached()> returns a new database handle if any of the
4292					attributes passed to is have changed. If we used an inline hash reference,
4293					C<connect_cached()> would return a new database handle every time. Which would
4294					rather defeat the purpose.
4295
4296					A more common application for callbacks is setting connection state only when
4297					a new connection is made (by connect() or connect_cached()). Adding a callback
4298					to the connected method (when using C<connect>) or via
4299					C<connect_cached.connected> (when useing connect_cached()>) makes this easy.
4300					The connected() method is a no-op by default (unless you subclass the DBI and
4301					change it). The DBI calls it to indicate that a new connection has been made
4302					and the connection attributes have all been set. You can give it a bit of
4303					added functionality by applying a callback to it. For example, to make sure
4304					that MySQL understands your application's ANSI-compliant SQL, set it up like
4305					so:
4306
4307					my $dbh = DBI->connect($dsn, $username, $auth, {
4308					Callbacks => {
4309					connected => sub {
4310					shift->do(q{
4311					SET SESSION sql_mode='ansi,strict_trans_tables,no_auto_value_on_zero';
4312					});
4313					return;
4314					},
4315					}
4316					});
4317
4318					If you're using C<connect_cached()>, use the C<connect_cached.connected>
4319					callback, instead. This is because C<connected()> is called for both new and
4320					reused database handles, but you want to execute a callback only the when a
4321					new database handle is returned. For example, to set the time zone on
4322					connection to a PostgreSQL database, try this:
4323
4324					my $cb = {
4325					'connect_cached.connected' => sub {
4326					shift->do('SET timezone = UTC');
4327					}
4328					};
4329
4330					sub dbh {
4331					my $self = shift;
4332					DBI->connect_cached( $dsn, $username, $auth, { Callbacks => $cb });
4333					}
4334
4335					One significant limitation with callbacks is that there can only be one per
4336					method per handle. This means it's easy for one use of callbacks to interfere
4337					with, or typically simply overwrite, another use of callbacks. For this reason
4338					modules using callbacks should document the fact clearly so application authors
4339					can tell if use of callbacks by the module will clash with use of callbacks by
4340					the application.
4341
4342					You might be able to work around this issue by taking a copy of the original
4343					callback and calling it within your own. For example:
4344
4345					my $prev_cb = $h->{Callbacks}{method_name};
4346					$h->{Callbacks}{method_name} = sub {
4347					if ($prev_cb) {
4348					my @result = $prev_cb->(@_);
4349					return @result if not $_; # $prev_cb vetoed call
4350					}
4351					... your callback logic here ...
4352					};
4353
4354					=head3 C<private_your_module_name_*>
4355
4356					The DBI provides a way to store extra information in a DBI handle as
4357					"private" attributes. The DBI will allow you to store and retrieve any
4358					attribute which has a name starting with "C<private_>".
4359
4360					It is I<strongly> recommended that you use just I<one> private
4361					attribute (e.g., use a hash ref) I<and> give it a long and unambiguous
4362					name that includes the module or application name that the attribute
4363					relates to (e.g., "C<private_YourFullModuleName_thingy>").
4364
4365					Because of the way the Perl tie mechanism works you cannot reliably
4366					use the C<\|\|=> operator directly to initialise the attribute, like this:
4367
4368					my $foo = $dbh->{private_yourmodname_foo} \|\|= { ... }; # WRONG
4369
4370					you should use a two step approach like this:
4371
4372					my $foo = $dbh->{private_yourmodname_foo};
4373					$foo \|\|= $dbh->{private_yourmodname_foo} = { ... };
4374
4375					This attribute is primarily of interest to people sub-classing DBI,
4376					or for applications to piggy-back extra information onto DBI handles.
4377
4378					=head1 DBI DATABASE HANDLE OBJECTS
4379
4380					This section covers the methods and attributes associated with
4381					database handles.
4382
4383					=head2 Database Handle Methods
4384
4385					The following methods are specified for DBI database handles:
4386
4387					=head3 C<clone>
4388
4389					$new_dbh = $dbh->clone(\%attr);
4390
4391					The C<clone> method duplicates the $dbh connection by connecting
4392					with the same parameters ($dsn, $user, $password) as originally used.
4393
4394					The attributes for the cloned connect are the same as those used
4395					for the I<original> connect, with any other attributes in C<\%attr>
4396					merged over them. Effectively the same as doing:
4397
4398					%attributes_used = ( %original_attributes, %attr );
4399
4400					If \%attr is not given then it defaults to a hash containing all
4401					the attributes in the attribute cache of $dbh excluding any non-code
4402					references, plus the main boolean attributes (RaiseError, PrintError,
4403					AutoCommit, etc.). I<This behaviour is unreliable and so use of clone without
4404					an argument is deprecated and may cause a warning in a future release.>
4405
4406					The clone method can be used even if the database handle is disconnected.
4407
4408					The C<clone> method was added in DBI 1.33.
4409
4410					=head3 C<data_sources>
4411
4412					@ary = $dbh->data_sources();
4413					@ary = $dbh->data_sources(\%attr);
4414
4415					Returns a list of data sources (databases) available via the $dbh
4416					driver's data_sources() method, plus any extra data sources that
4417					the driver can discover via the connected $dbh. Typically the extra
4418					data sources are other databases managed by the same server process
4419					that the $dbh is connected to.
4420
4421					Data sources are returned in a form suitable for passing to the
4422					L</connect> method (that is, they will include the "C<dbi:$driver:>" prefix).
4423
4424					The data_sources() method, for a $dbh, was added in DBI 1.38.
4425
4426					=head3 C<do>
4427
4428					$rows = $dbh->do($statement) or die $dbh->errstr;
4429					$rows = $dbh->do($statement, \%attr) or die $dbh->errstr;
4430					$rows = $dbh->do($statement, \%attr, @bind_values) or die ...
4431
4432					Prepare and execute a single statement. Returns the number of rows
4433					affected or C<undef> on error. A return value of C<-1> means the
4434					number of rows is not known, not applicable, or not available.
4435
4436					This method is typically most useful for I<non>-C<SELECT> statements that
4437					either cannot be prepared in advance (due to a limitation of the
4438					driver) or do not need to be executed repeatedly. It should not
4439					be used for C<SELECT> statements because it does not return a statement
4440					handle (so you can't fetch any data).
4441
4442					The default C<do> method is logically similar to:
4443
4444					sub do {
4445					my($dbh, $statement, $attr, @bind_values) = @_;
4446					my $sth = $dbh->prepare($statement, $attr) or return undef;
4447					$sth->execute(@bind_values) or return undef;
4448					my $rows = $sth->rows;
4449					($rows == 0) ? "0E0" : $rows; # always return true if no error
4450					}
4451
4452					For example:
4453
4454					my $rows_deleted = $dbh->do(q{
4455					DELETE FROM table
4456					WHERE status = ?
4457					}, undef, 'DONE') or die $dbh->errstr;
4458
4459					Using placeholders and C<@bind_values> with the C<do> method can be
4460					useful because it avoids the need to correctly quote any variables
4461					in the C<$statement>. But if you'll be executing the statement many
4462					times then it's more efficient to C<prepare> it once and call
4463					C<execute> many times instead.
4464
4465					The C<q{...}> style quoting used in this example avoids clashing with
4466					quotes that may be used in the SQL statement. Use the double-quote-like
4467					C<qq{...}> operator if you want to interpolate variables into the string.
4468					See L<perlop/"Quote and Quote-like Operators"> for more details.
4469
4470					Note drivers are free to avoid the overhead of creating an DBI
4471					statement handle for do(), especially if there are no parameters. In
4472					this case error handlers, if invoked during do(), will be passed the
4473					database handle.
4474
4475					=head3 C<last_insert_id>
4476
4477					$rv = $dbh->last_insert_id($catalog, $schema, $table, $field);
4478					$rv = $dbh->last_insert_id($catalog, $schema, $table, $field, \%attr);
4479
4480					Returns a value 'identifying' the row just inserted, if possible.
4481					Typically this would be a value assigned by the database server
4482					to a column with an I<auto_increment> or I<serial> type.
4483					Returns undef if the driver does not support the method or can't
4484					determine the value.
4485
4486					The $catalog, $schema, $table, and $field parameters may be required
4487					for some drivers (see below). If you don't know the parameter values
4488					and your driver does not need them, then use C<undef> for each.
4489
4490					There are several caveats to be aware of with this method if you want
4491					to use it for portable applications:
4492
4493					B<*> For some drivers the value may only available immediately after
4494					the insert statement has executed (e.g., mysql, Informix).
4495
4496					B<*> For some drivers the $catalog, $schema, $table, and $field parameters
4497					are required, for others they are ignored (e.g., mysql).
4498
4499					B<*> Drivers may return an indeterminate value if no insert has
4500					been performed yet.
4501
4502					B<*> For some drivers the value may only be available if placeholders
4503					have I<not> been used (e.g., Sybase, MS SQL). In this case the value
4504					returned would be from the last non-placeholder insert statement.
4505
4506					B<*> Some drivers may need driver-specific hints about how to get
4507					the value. For example, being told the name of the database 'sequence'
4508					object that holds the value. Any such hints are passed as driver-specific
4509					attributes in the \%attr parameter.
4510
4511					B<*> If the underlying database offers nothing better, then some
4512					drivers may attempt to implement this method by executing
4513					"C<select max($field) from $table>". Drivers using any approach
4514					like this should issue a warning if C<AutoCommit> is true because
4515					it is generally unsafe - another process may have modified the table
4516					between your insert and the select. For situations where you know
4517					it is safe, such as when you have locked the table, you can silence
4518					the warning by passing C<Warn> => 0 in \%attr.
4519
4520					B<*> If no insert has been performed yet, or the last insert failed,
4521					then the value is implementation defined.
4522
4523					Given all the caveats above, it's clear that this method must be
4524					used with care.
4525
4526					The C<last_insert_id> method was added in DBI 1.38.
4527
4528					=head3 C<selectrow_array>
4529
4530					@row_ary = $dbh->selectrow_array($statement);
4531					@row_ary = $dbh->selectrow_array($statement, \%attr);
4532					@row_ary = $dbh->selectrow_array($statement, \%attr, @bind_values);
4533
4534					This utility method combines L</prepare>, L</execute> and
4535					L</fetchrow_array> into a single call. If called in a list context, it
4536					returns the first row of data from the statement. The C<$statement>
4537					parameter can be a previously prepared statement handle, in which case
4538					the C<prepare> is skipped.
4539
4540					If any method fails, and L</RaiseError> is not set, C<selectrow_array>
4541					will return an empty list.
4542
4543					If called in a scalar context for a statement handle that has more
4544					than one column, it is undefined whether the driver will return
4545					the value of the first column or the last. So don't do that.
4546					Also, in a scalar context, an C<undef> is returned if there are no
4547					more rows or if an error occurred. That C<undef> can't be distinguished
4548					from an C<undef> returned because the first field value was NULL.
4549					For these reasons you should exercise some caution if you use
4550					C<selectrow_array> in a scalar context, or just don't do that.
4551
4552
4553					=head3 C<selectrow_arrayref>
4554
4555					$ary_ref = $dbh->selectrow_arrayref($statement);
4556					$ary_ref = $dbh->selectrow_arrayref($statement, \%attr);
4557					$ary_ref = $dbh->selectrow_arrayref($statement, \%attr, @bind_values);
4558
4559					This utility method combines L</prepare>, L</execute> and
4560					L</fetchrow_arrayref> into a single call. It returns the first row of
4561					data from the statement. The C<$statement> parameter can be a previously
4562					prepared statement handle, in which case the C<prepare> is skipped.
4563
4564					If any method fails, and L</RaiseError> is not set, C<selectrow_array>
4565					will return undef.
4566
4567
4568					=head3 C<selectrow_hashref>
4569
4570					$hash_ref = $dbh->selectrow_hashref($statement);
4571					$hash_ref = $dbh->selectrow_hashref($statement, \%attr);
4572					$hash_ref = $dbh->selectrow_hashref($statement, \%attr, @bind_values);
4573
4574					This utility method combines L</prepare>, L</execute> and
4575					L</fetchrow_hashref> into a single call. It returns the first row of
4576					data from the statement. The C<$statement> parameter can be a previously
4577					prepared statement handle, in which case the C<prepare> is skipped.
4578
4579					If any method fails, and L</RaiseError> is not set, C<selectrow_hashref>
4580					will return undef.
4581
4582
4583					=head3 C<selectall_arrayref>
4584
4585					$ary_ref = $dbh->selectall_arrayref($statement);
4586					$ary_ref = $dbh->selectall_arrayref($statement, \%attr);
4587					$ary_ref = $dbh->selectall_arrayref($statement, \%attr, @bind_values);
4588
4589					This utility method combines L</prepare>, L</execute> and
4590					L</fetchall_arrayref> into a single call. It returns a reference to an
4591					array containing a reference to an array (or hash, see below) for each row of
4592					data fetched.
4593
4594					The C<$statement> parameter can be a previously prepared statement handle,
4595					in which case the C<prepare> is skipped. This is recommended if the
4596					statement is going to be executed many times.
4597
4598					If L</RaiseError> is not set and any method except C<fetchall_arrayref>
4599					fails then C<selectall_arrayref> will return C<undef>; if
4600					C<fetchall_arrayref> fails then it will return with whatever data
4601					has been fetched thus far. You should check C<$dbh-E<gt>err>
4602					afterwards (or use the C<RaiseError> attribute) to discover if the data is
4603					complete or was truncated due to an error.
4604
4605					The L</fetchall_arrayref> method called by C<selectall_arrayref>
4606					supports a $max_rows parameter. You can specify a value for $max_rows
4607					by including a 'C<MaxRows>' attribute in \%attr. In which case finish()
4608					is called for you after fetchall_arrayref() returns.
4609
4610					The L</fetchall_arrayref> method called by C<selectall_arrayref>
4611					also supports a $slice parameter. You can specify a value for $slice by
4612					including a 'C<Slice>' or 'C<Columns>' attribute in \%attr. The only
4613					difference between the two is that if C<Slice> is not defined and
4614					C<Columns> is an array ref, then the array is assumed to contain column
4615					index values (which count from 1), rather than perl array index values.
4616					In which case the array is copied and each value decremented before
4617					passing to C</fetchall_arrayref>.
4618
4619					You may often want to fetch an array of rows where each row is stored as a
4620					hash. That can be done simple using:
4621
4622					my $emps = $dbh->selectall_arrayref(
4623					"SELECT ename FROM emp ORDER BY ename",
4624					{ Slice => {} }
4625					);
4626					foreach my $emp ( @$emps ) {
4627					print "Employee: $emp->{ename}\n";
4628					}
4629
4630					Or, to fetch into an array instead of an array ref:
4631
4632					@result = @{ $dbh->selectall_arrayref($sql, { Slice => {} }) };
4633
4634					See L</fetchall_arrayref> method for more details.
4635
4636					=head3 C<selectall_hashref>
4637
4638					$hash_ref = $dbh->selectall_hashref($statement, $key_field);
4639					$hash_ref = $dbh->selectall_hashref($statement, $key_field, \%attr);
4640					$hash_ref = $dbh->selectall_hashref($statement, $key_field, \%attr, @bind_values);
4641
4642					This utility method combines L</prepare>, L</execute> and
4643					L</fetchall_hashref> into a single call. It returns a reference to a
4644					hash containing one entry, at most, for each row, as returned by fetchall_hashref().
4645
4646					The C<$statement> parameter can be a previously prepared statement handle,
4647					in which case the C<prepare> is skipped. This is recommended if the
4648					statement is going to be executed many times.
4649
4650					The C<$key_field> parameter defines which column, or columns, are used as keys
4651					in the returned hash. It can either be the name of a single field, or a
4652					reference to an array containing multiple field names. Using multiple names
4653					yields a tree of nested hashes.
4654
4655					If a row has the same key as an earlier row then it replaces the earlier row.
4656
4657					If any method except C<fetchrow_hashref> fails, and L</RaiseError> is not set,
4658					C<selectall_hashref> will return C<undef>. If C<fetchrow_hashref> fails and
4659					L</RaiseError> is not set, then it will return with whatever data it
4660					has fetched thus far. $DBI::err should be checked to catch that.
4661
4662					See fetchall_hashref() for more details.
4663
4664					=head3 C<selectcol_arrayref>
4665
4666					$ary_ref = $dbh->selectcol_arrayref($statement);
4667					$ary_ref = $dbh->selectcol_arrayref($statement, \%attr);
4668					$ary_ref = $dbh->selectcol_arrayref($statement, \%attr, @bind_values);
4669
4670					This utility method combines L</prepare>, L</execute>, and fetching one
4671					column from all the rows, into a single call. It returns a reference to
4672					an array containing the values of the first column from each row.
4673
4674					The C<$statement> parameter can be a previously prepared statement handle,
4675					in which case the C<prepare> is skipped. This is recommended if the
4676					statement is going to be executed many times.
4677
4678					If any method except C<fetch> fails, and L</RaiseError> is not set,
4679					C<selectcol_arrayref> will return C<undef>. If C<fetch> fails and
4680					L</RaiseError> is not set, then it will return with whatever data it
4681					has fetched thus far. $DBI::err should be checked to catch that.
4682
4683					The C<selectcol_arrayref> method defaults to pushing a single column
4684					value (the first) from each row into the result array. However, it can
4685					also push another column, or even multiple columns per row, into the
4686					result array. This behaviour can be specified via a 'C<Columns>'
4687					attribute which must be a ref to an array containing the column number
4688					or numbers to use. For example:
4689
4690					# get array of id and name pairs:
4691					my $ary_ref = $dbh->selectcol_arrayref("select id, name from table", { Columns=>[1,2] });
4692					my %hash = @$ary_ref; # build hash from key-value pairs so $hash{$id} => name
4693
4694					You can specify a maximum number of rows to fetch by including a
4695					'C<MaxRows>' attribute in \%attr.
4696
4697					=head3 C<prepare>
4698
4699					$sth = $dbh->prepare($statement) or die $dbh->errstr;
4700					$sth = $dbh->prepare($statement, \%attr) or die $dbh->errstr;
4701
4702					Prepares a statement for later execution by the database
4703					engine and returns a reference to a statement handle object.
4704
4705					The returned statement handle can be used to get attributes of the
4706					statement and invoke the L</execute> method. See L</Statement Handle Methods>.
4707
4708					Drivers for engines without the concept of preparing a
4709					statement will typically just store the statement in the returned
4710					handle and process it when C<$sth-E<gt>execute> is called. Such drivers are
4711					unlikely to give much useful information about the
4712					statement, such as C<$sth-E<gt>{NUM_OF_FIELDS}>, until after C<$sth-E<gt>execute>
4713					has been called. Portable applications should take this into account.
4714
4715					In general, DBI drivers do not parse the contents of the statement
4716					(other than simply counting any L</Placeholders>). The statement is
4717					passed directly to the database engine, sometimes known as pass-thru
4718					mode. This has advantages and disadvantages. On the plus side, you can
4719					access all the functionality of the engine being used. On the downside,
4720					you're limited if you're using a simple engine, and you need to take extra care if
4721					writing applications intended to be portable between engines.
4722
4723					Portable applications should not assume that a new statement can be
4724					prepared and/or executed while still fetching results from a previous
4725					statement.
4726
4727					Some command-line SQL tools use statement terminators, like a semicolon,
4728					to indicate the end of a statement. Such terminators should not normally
4729					be used with the DBI.
4730
4731
4732					=head3 C<prepare_cached>
4733
4734					$sth = $dbh->prepare_cached($statement)
4735					$sth = $dbh->prepare_cached($statement, \%attr)
4736					$sth = $dbh->prepare_cached($statement, \%attr, $if_active)
4737
4738					Like L</prepare> except that the statement handle returned will be
4739					stored in a hash associated with the C<$dbh>. If another call is made to
4740					C<prepare_cached> with the same C<$statement> and C<%attr> parameter values,
4741					then the corresponding cached C<$sth> will be returned without contacting the
4742					database server.
4743
4744					The C<$if_active> parameter lets you adjust the behaviour if an
4745					already cached statement handle is still Active. There are several
4746					alternatives:
4747
4748					=over 4
4749
4750					=item B<0>: A warning will be generated, and finish() will be called on
4751					the statement handle before it is returned. This is the default
4752					behaviour if $if_active is not passed.
4753
4754					=item B<1>: finish() will be called on the statement handle, but the
4755					warning is suppressed.
4756
4757					=item B<2>: Disables any checking.
4758
4759					=item B<3>: The existing active statement handle will be removed from the
4760					cache and a new statement handle prepared and cached in its place.
4761					This is the safest option because it doesn't affect the state of the
4762					old handle, it just removes it from the cache. [Added in DBI 1.40]
4763
4764					=back
4765
4766					Here are some examples of C<prepare_cached>:
4767
4768					sub insert_hash {
4769					my ($table, $field_values) = @_;
4770					# sort to keep field order, and thus sql, stable for prepare_cached
4771					my @fields = sort keys %$field_values;
4772					my @values = @{$field_values}{@fields};
4773					my $sql = sprintf "insert into %s (%s) values (%s)",
4774					$table, join(",", @fields), join(",", ("?")x@fields);
4775					my $sth = $dbh->prepare_cached($sql);
4776					return $sth->execute(@values);
4777					}
4778
4779					sub search_hash {
4780					my ($table, $field_values) = @_;
4781					# sort to keep field order, and thus sql, stable for prepare_cached
4782					my @fields = sort keys %$field_values;
4783					my @values = @{$field_values}{@fields};
4784					my $qualifier = "";
4785					$qualifier = "where ".join(" and ", map { "$_=?" } @fields) if @fields;
4786					$sth = $dbh->prepare_cached("SELECT * FROM $table $qualifier");
4787					return $dbh->selectall_arrayref($sth, {}, @values);
4788					}
4789
4790					I<Caveat emptor:> This caching can be useful in some applications,
4791					but it can also cause problems and should be used with care. Here
4792					is a contrived case where caching would cause a significant problem:
4793
4794					my $sth = $dbh->prepare_cached('SELECT * FROM foo WHERE bar=?');
4795					$sth->execute(...);
4796					while (my $data = $sth->fetchrow_hashref) {
4797
4798					# later, in some other code called within the loop...
4799					my $sth2 = $dbh->prepare_cached('SELECT * FROM foo WHERE bar=?');
4800					$sth2->execute(...);
4801					while (my $data2 = $sth2->fetchrow_arrayref) {
4802					do_stuff(...);
4803					}
4804					}
4805
4806					In this example, since both handles are preparing the exact same statement,
4807					C<$sth2> will not be its own statement handle, but a duplicate of C<$sth>
4808					returned from the cache. The results will certainly not be what you expect.
4809					Typically the inner fetch loop will work normally, fetching all
4810					the records and terminating when there are no more, but now that $sth
4811					is the same as $sth2 the outer fetch loop will also terminate.
4812
4813					You'll know if you run into this problem because prepare_cached()
4814					will generate a warning by default (when $if_active is false).
4815
4816					The cache used by prepare_cached() is keyed by both the statement
4817					and any attributes so you can also avoid this issue by doing something
4818					like:
4819
4820					$sth = $dbh->prepare_cached("...", { dbi_dummy => __FILE__.__LINE__ });
4821
4822					which will ensure that prepare_cached only returns statements cached
4823					by that line of code in that source file.
4824
4825					If you'd like the cache to managed intelligently, you can tie the
4826					hashref returned by C<CachedKids> to an appropriate caching module,
4827					such as L<Tie::Cache::LRU>:
4828
4829					my $cache;
4830					tie %$cache, 'Tie::Cache::LRU', 500;
4831					$dbh->{CachedKids} = $cache;
4832
4833					=head3 C<commit>
4834
4835					$rc = $dbh->commit or die $dbh->errstr;
4836
4837					Commit (make permanent) the most recent series of database changes
4838					if the database supports transactions and AutoCommit is off.
4839
4840					If C<AutoCommit> is on, then calling
4841					C<commit> will issue a "commit ineffective with AutoCommit" warning.
4842
4843					See also L</Transactions> in the L</FURTHER INFORMATION> section below.
4844
4845					=head3 C<rollback>
4846
4847					$rc = $dbh->rollback or die $dbh->errstr;
4848
4849					Rollback (undo) the most recent series of uncommitted database
4850					changes if the database supports transactions and AutoCommit is off.
4851
4852					If C<AutoCommit> is on, then calling
4853					C<rollback> will issue a "rollback ineffective with AutoCommit" warning.
4854
4855					See also L</Transactions> in the L</FURTHER INFORMATION> section below.
4856
4857					=head3 C<begin_work>
4858
4859					$rc = $dbh->begin_work or die $dbh->errstr;
4860
4861					Enable transactions (by turning C<AutoCommit> off) until the next call
4862					to C<commit> or C<rollback>. After the next C<commit> or C<rollback>,
4863					C<AutoCommit> will automatically be turned on again.
4864
4865					If C<AutoCommit> is already off when C<begin_work> is called then
4866					it does nothing except return an error. If the driver does not support
4867					transactions then when C<begin_work> attempts to set C<AutoCommit> off
4868					the driver will trigger a fatal error.
4869
4870					See also L</Transactions> in the L</FURTHER INFORMATION> section below.
4871
4872
4873					=head3 C<disconnect>
4874
4875					$rc = $dbh->disconnect or warn $dbh->errstr;
4876
4877					Disconnects the database from the database handle. C<disconnect> is typically only used
4878					before exiting the program. The handle is of little use after disconnecting.
4879
4880					The transaction behaviour of the C<disconnect> method is, sadly,
4881					undefined. Some database systems (such as Oracle and Ingres) will
4882					automatically commit any outstanding changes, but others (such as
4883					Informix) will rollback any outstanding changes. Applications not
4884					using C<AutoCommit> should explicitly call C<commit> or C<rollback> before
4885					calling C<disconnect>.
4886
4887					The database is automatically disconnected by the C<DESTROY> method if
4888					still connected when there are no longer any references to the handle.
4889					The C<DESTROY> method for each driver should implicitly call C<rollback> to
4890					undo any uncommitted changes. This is vital behaviour to ensure that
4891					incomplete transactions don't get committed simply because Perl calls
4892					C<DESTROY> on every object before exiting. Also, do not rely on the order
4893					of object destruction during "global destruction", as it is undefined.
4894
4895					Generally, if you want your changes to be committed or rolled back when
4896					you disconnect, then you should explicitly call L</commit> or L</rollback>
4897					before disconnecting.
4898
4899					If you disconnect from a database while you still have active
4900					statement handles (e.g., SELECT statement handles that may have
4901					more data to fetch), you will get a warning. The warning may indicate
4902					that a fetch loop terminated early, perhaps due to an uncaught error.
4903					To avoid the warning call the C<finish> method on the active handles.
4904
4905
4906					=head3 C<ping>
4907
4908					$rc = $dbh->ping;
4909
4910					Attempts to determine, in a reasonably efficient way, if the database
4911					server is still running and the connection to it is still working.
4912					Individual drivers should implement this function in the most suitable
4913					manner for their database engine.
4914
4915					The current I<default> implementation always returns true without
4916					actually doing anything. Actually, it returns "C<0 but true>" which is
4917					true but zero. That way you can tell if the return value is genuine or
4918					just the default. Drivers should override this method with one that
4919					does the right thing for their type of database.
4920
4921					Few applications would have direct use for this method. See the specialized
4922					Apache::DBI module for one example usage.
4923
4924
4925					=head3 C<get_info>
4926
4927					$value = $dbh->get_info( $info_type );
4928
4929					Returns information about the implementation, i.e. driver and data
4930					source capabilities, restrictions etc. It returns C<undef> for
4931					unknown or unimplemented information types. For example:
4932
4933					$database_version = $dbh->get_info( 18 ); # SQL_DBMS_VER
4934					$max_select_tables = $dbh->get_info( 106 ); # SQL_MAXIMUM_TABLES_IN_SELECT
4935
4936					See L</"Standards Reference Information"> for more detailed information
4937					about the information types and their meanings and possible return values.
4938
4939					The DBI::Const::GetInfoType module exports a %GetInfoType hash that
4940					can be used to map info type names to numbers. For example:
4941
4942					$database_version = $dbh->get_info( $GetInfoType{SQL_DBMS_VER} );
4943
4944					The names are a merging of the ANSI and ODBC standards (which differ
4945					in some cases). See L<DBI::Const::GetInfoType> for more details.
4946
4947					Because some DBI methods make use of get_info(), drivers are strongly
4948					encouraged to support I<at least> the following very minimal set
4949					of information types to ensure the DBI itself works properly:
4950
4951					Type Name Example A Example B
4952					---- -------------------------- ------------ ----------------
4953					17 SQL_DBMS_NAME 'ACCESS' 'Oracle'
4954					18 SQL_DBMS_VER '03.50.0000' '08.01.0721 ...'
4955					29 SQL_IDENTIFIER_QUOTE_CHAR '`' '"'
4956					41 SQL_CATALOG_NAME_SEPARATOR '.' '@'
4957					114 SQL_CATALOG_LOCATION 1 2
4958
4959					=head3 C<table_info>
4960
4961					$sth = $dbh->table_info( $catalog, $schema, $table, $type );
4962					$sth = $dbh->table_info( $catalog, $schema, $table, $type, \%attr );
4963
4964					# then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
4965
4966					Returns an active statement handle that can be used to fetch
4967					information about tables and views that exist in the database.
4968
4969					The arguments $catalog, $schema and $table may accept search patterns
4970					according to the database/driver, for example: $table = '%FOO%';
4971					Remember that the underscore character ('C<_>') is a search pattern
4972					that means match any character, so 'FOO_%' is the same as 'FOO%'
4973					and 'FOO_BAR%' will match names like 'FOO1BAR'.
4974
4975					The value of $type is a comma-separated list of one or more types of
4976					tables to be returned in the result set. Each value may optionally be
4977					quoted, e.g.:
4978
4979					$type = "TABLE";
4980					$type = "'TABLE','VIEW'";
4981
4982					In addition the following special cases may also be supported by some drivers:
4983
4984					=over 4
4985
4986					=item *
4987					If the value of $catalog is '%' and $schema and $table name
4988					are empty strings, the result set contains a list of catalog names.
4989					For example:
4990
4991					$sth = $dbh->table_info('%', '', '');
4992
4993					=item *
4994					If the value of $schema is '%' and $catalog and $table are empty
4995					strings, the result set contains a list of schema names.
4996
4997					=item *
4998					If the value of $type is '%' and $catalog, $schema, and $table are all
4999					empty strings, the result set contains a list of table types.
5000
5001					=back
5002
5003					If your driver doesn't support one or more of the selection filter
5004					parameters then you may get back more than you asked for and can
5005					do the filtering yourself.
5006
5007					This method can be expensive, and can return a large amount of data.
5008					(For example, small Oracle installation returns over 2000 rows.)
5009					So it's a good idea to use the filters to limit the data as much as possible.
5010
5011					The statement handle returned has at least the following fields in the
5012					order show below. Other fields, after these, may also be present.
5013
5014					B<TABLE_CAT>: Table catalog identifier. This field is NULL (C<undef>) if not
5015					applicable to the data source, which is usually the case. This field
5016					is empty if not applicable to the table.
5017
5018					B<TABLE_SCHEM>: The name of the schema containing the TABLE_NAME value.
5019					This field is NULL (C<undef>) if not applicable to data source, and
5020					empty if not applicable to the table.
5021
5022					B<TABLE_NAME>: Name of the table (or view, synonym, etc).
5023
5024					B<TABLE_TYPE>: One of the following: "TABLE", "VIEW", "SYSTEM TABLE",
5025					"GLOBAL TEMPORARY", "LOCAL TEMPORARY", "ALIAS", "SYNONYM" or a type
5026					identifier that is specific to the data
5027					source.
5028
5029					B<REMARKS>: A description of the table. May be NULL (C<undef>).
5030
5031					Note that C<table_info> might not return records for all tables.
5032					Applications can use any valid table regardless of whether it's
5033					returned by C<table_info>.
5034
5035					See also L</tables>, L</"Catalog Methods"> and
5036					L</"Standards Reference Information">.
5037
5038					=head3 C<column_info>
5039
5040					$sth = $dbh->column_info( $catalog, $schema, $table, $column );
5041
5042					# then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
5043
5044					Returns an active statement handle that can be used to fetch
5045					information about columns in specified tables.
5046
5047					The arguments $schema, $table and $column may accept search patterns
5048					according to the database/driver, for example: $table = '%FOO%';
5049
5050					Note: The support for the selection criteria is driver specific. If the
5051					driver doesn't support one or more of them then you may get back more
5052					than you asked for and can do the filtering yourself.
5053
5054					Note: If your driver does not support column_info an undef is
5055					returned. This is distinct from asking for something which does not
5056					exist in a driver which supports column_info as a valid statement
5057					handle to an empty result-set will be returned in this case.
5058
5059					If the arguments don't match any tables then you'll still get a statement
5060					handle, it'll just return no rows.
5061
5062					The statement handle returned has at least the following fields in the
5063					order shown below. Other fields, after these, may also be present.
5064
5065					B<TABLE_CAT>: The catalog identifier.
5066					This field is NULL (C<undef>) if not applicable to the data source,
5067					which is often the case. This field is empty if not applicable to the
5068					table.
5069
5070					B<TABLE_SCHEM>: The schema identifier.
5071					This field is NULL (C<undef>) if not applicable to the data source,
5072					and empty if not applicable to the table.
5073
5074					B<TABLE_NAME>: The table identifier.
5075					Note: A driver may provide column metadata not only for base tables, but
5076					also for derived objects like SYNONYMS etc.
5077
5078					B<COLUMN_NAME>: The column identifier.
5079
5080					B<DATA_TYPE>: The concise data type code.
5081
5082					B<TYPE_NAME>: A data source dependent data type name.
5083
5084					B<COLUMN_SIZE>: The column size.
5085					This is the maximum length in characters for character data types,
5086					the number of digits or bits for numeric data types or the length
5087					in the representation of temporal types.
5088					See the relevant specifications for detailed information.
5089
5090					B<BUFFER_LENGTH>: The length in bytes of transferred data.
5091
5092					B<DECIMAL_DIGITS>: The total number of significant digits to the right of
5093					the decimal point.
5094
5095					B<NUM_PREC_RADIX>: The radix for numeric precision.
5096					The value is 10 or 2 for numeric data types and NULL (C<undef>) if not
5097					applicable.
5098
5099					B<NULLABLE>: Indicates if a column can accept NULLs.
5100					The following values are defined:
5101
5102					SQL_NO_NULLS 0
5103					SQL_NULLABLE 1
5104					SQL_NULLABLE_UNKNOWN 2
5105
5106					B<REMARKS>: A description of the column.
5107
5108					B<COLUMN_DEF>: The default value of the column, in a format that can be used
5109					directly in an SQL statement.
5110
5111					Note that this may be an expression and not simply the text used for the
5112					default value in the original CREATE TABLE statement. For example, given:
5113
5114					col1 char(30) default current_user -- a 'function'
5115					col2 char(30) default 'string' -- a string literal
5116
5117					where "current_user" is the name of a function, the corresponding C<COLUMN_DEF>
5118					values would be:
5119
5120					Database col1 col2
5121					-------- ---- ----
5122					Oracle: current_user 'string'
5123					Postgres: "current_user"() 'string'::text
5124					MS SQL: (user_name()) ('string')
5125
5126					B<SQL_DATA_TYPE>: The SQL data type.
5127
5128					B<SQL_DATETIME_SUB>: The subtype code for datetime and interval data types.
5129
5130					B<CHAR_OCTET_LENGTH>: The maximum length in bytes of a character or binary
5131					data type column.
5132
5133					B<ORDINAL_POSITION>: The column sequence number (starting with 1).
5134
5135					B<IS_NULLABLE>: Indicates if the column can accept NULLs.
5136					Possible values are: 'NO', 'YES' and ''.
5137
5138					SQL/CLI defines the following additional columns:
5139
5140					CHAR_SET_CAT
5141					CHAR_SET_SCHEM
5142					CHAR_SET_NAME
5143					COLLATION_CAT
5144					COLLATION_SCHEM
5145					COLLATION_NAME
5146					UDT_CAT
5147					UDT_SCHEM
5148					UDT_NAME
5149					DOMAIN_CAT
5150					DOMAIN_SCHEM
5151					DOMAIN_NAME
5152					SCOPE_CAT
5153					SCOPE_SCHEM
5154					SCOPE_NAME
5155					MAX_CARDINALITY
5156					DTD_IDENTIFIER
5157					IS_SELF_REF
5158
5159					Drivers capable of supplying any of those values should do so in
5160					the corresponding column and supply undef values for the others.
5161
5162					Drivers wishing to provide extra database/driver specific information
5163					should do so in extra columns beyond all those listed above, and
5164					use lowercase field names with the driver-specific prefix (i.e.,
5165					'ora_...'). Applications accessing such fields should do so by name
5166					and not by column number.
5167
5168					The result set is ordered by TABLE_CAT, TABLE_SCHEM, TABLE_NAME
5169					and ORDINAL_POSITION.
5170
5171					Note: There is some overlap with statement handle attributes (in perl) and
5172					SQLDescribeCol (in ODBC). However, SQLColumns provides more metadata.
5173
5174					See also L</"Catalog Methods"> and L</"Standards Reference Information">.
5175
5176					=head3 C<primary_key_info>
5177
5178					$sth = $dbh->primary_key_info( $catalog, $schema, $table );
5179
5180					# then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
5181
5182					Returns an active statement handle that can be used to fetch information
5183					about columns that make up the primary key for a table.
5184					The arguments don't accept search patterns (unlike table_info()).
5185
5186					The statement handle will return one row per column, ordered by
5187					TABLE_CAT, TABLE_SCHEM, TABLE_NAME, and KEY_SEQ.
5188					If there is no primary key then the statement handle will fetch no rows.
5189
5190					Note: The support for the selection criteria, such as $catalog, is
5191					driver specific. If the driver doesn't support catalogs and/or
5192					schemas, it may ignore these criteria.
5193
5194					The statement handle returned has at least the following fields in the
5195					order shown below. Other fields, after these, may also be present.
5196
5197					B<TABLE_CAT>: The catalog identifier.
5198					This field is NULL (C<undef>) if not applicable to the data source,
5199					which is often the case. This field is empty if not applicable to the
5200					table.
5201
5202					B<TABLE_SCHEM>: The schema identifier.
5203					This field is NULL (C<undef>) if not applicable to the data source,
5204					and empty if not applicable to the table.
5205
5206					B<TABLE_NAME>: The table identifier.
5207
5208					B<COLUMN_NAME>: The column identifier.
5209
5210					B<KEY_SEQ>: The column sequence number (starting with 1).
5211					Note: This field is named B<ORDINAL_POSITION> in SQL/CLI.
5212
5213					B<PK_NAME>: The primary key constraint identifier.
5214					This field is NULL (C<undef>) if not applicable to the data source.
5215
5216					See also L</"Catalog Methods"> and L</"Standards Reference Information">.
5217
5218					=head3 C<primary_key>
5219
5220					@key_column_names = $dbh->primary_key( $catalog, $schema, $table );
5221
5222					Simple interface to the primary_key_info() method. Returns a list of
5223					the column names that comprise the primary key of the specified table.
5224					The list is in primary key column sequence order.
5225					If there is no primary key then an empty list is returned.
5226
5227					=head3 C<foreign_key_info>
5228
5229					$sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
5230					, $fk_catalog, $fk_schema, $fk_table );
5231
5232					$sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
5233					, $fk_catalog, $fk_schema, $fk_table
5234					, \%attr );
5235
5236					# then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
5237
5238					Returns an active statement handle that can be used to fetch information
5239					about foreign keys in and/or referencing the specified table(s).
5240					The arguments don't accept search patterns (unlike table_info()).
5241
5242					C<$pk_catalog>, C<$pk_schema>, C<$pk_table>
5243					identify the primary (unique) key table (B<PKT>).
5244
5245					C<$fk_catalog>, C<$fk_schema>, C<$fk_table>
5246					identify the foreign key table (B<FKT>).
5247
5248					If both B<PKT> and B<FKT> are given, the function returns the foreign key, if
5249					any, in table B<FKT> that refers to the primary (unique) key of table B<PKT>.
5250					(Note: In SQL/CLI, the result is implementation-defined.)
5251
5252					If only B<PKT> is given, then the result set contains the primary key
5253					of that table and all foreign keys that refer to it.
5254
5255					If only B<FKT> is given, then the result set contains all foreign keys
5256					in that table and the primary keys to which they refer.
5257					(Note: In SQL/CLI, the result includes unique keys too.)
5258
5259					For example:
5260
5261					$sth = $dbh->foreign_key_info( undef, $user, 'master');
5262					$sth = $dbh->foreign_key_info( undef, undef, undef , undef, $user, 'detail');
5263					$sth = $dbh->foreign_key_info( undef, $user, 'master', undef, $user, 'detail');
5264
5265					# then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
5266
5267					Note: The support for the selection criteria, such as C<$catalog>, is
5268					driver specific. If the driver doesn't support catalogs and/or
5269					schemas, it may ignore these criteria.
5270
5271					The statement handle returned has the following fields in the order shown below.
5272					Because ODBC never includes unique keys, they define different columns in the
5273					result set than SQL/CLI. SQL/CLI column names are shown in parentheses.
5274
5275					B<PKTABLE_CAT ( UK_TABLE_CAT )>:
5276					The primary (unique) key table catalog identifier.
5277					This field is NULL (C<undef>) if not applicable to the data source,
5278					which is often the case. This field is empty if not applicable to the
5279					table.
5280
5281					B<PKTABLE_SCHEM ( UK_TABLE_SCHEM )>:
5282					The primary (unique) key table schema identifier.
5283					This field is NULL (C<undef>) if not applicable to the data source,
5284					and empty if not applicable to the table.
5285
5286					B<PKTABLE_NAME ( UK_TABLE_NAME )>:
5287					The primary (unique) key table identifier.
5288
5289					B<PKCOLUMN_NAME (UK_COLUMN_NAME )>:
5290					The primary (unique) key column identifier.
5291
5292					B<FKTABLE_CAT ( FK_TABLE_CAT )>:
5293					The foreign key table catalog identifier.
5294					This field is NULL (C<undef>) if not applicable to the data source,
5295					which is often the case. This field is empty if not applicable to the
5296					table.
5297
5298					B<FKTABLE_SCHEM ( FK_TABLE_SCHEM )>:
5299					The foreign key table schema identifier.
5300					This field is NULL (C<undef>) if not applicable to the data source,
5301					and empty if not applicable to the table.
5302
5303					B<FKTABLE_NAME ( FK_TABLE_NAME )>:
5304					The foreign key table identifier.
5305
5306					B<FKCOLUMN_NAME ( FK_COLUMN_NAME )>:
5307					The foreign key column identifier.
5308
5309					B<KEY_SEQ ( ORDINAL_POSITION )>:
5310					The column sequence number (starting with 1).
5311
5312					B<UPDATE_RULE ( UPDATE_RULE )>:
5313					The referential action for the UPDATE rule.
5314					The following codes are defined:
5315
5316					CASCADE 0
5317					RESTRICT 1
5318					SET NULL 2
5319					NO ACTION 3
5320					SET DEFAULT 4
5321
5322					B<DELETE_RULE ( DELETE_RULE )>:
5323					The referential action for the DELETE rule.
5324					The codes are the same as for UPDATE_RULE.
5325
5326					B<FK_NAME ( FK_NAME )>:
5327					The foreign key name.
5328
5329					B<PK_NAME ( UK_NAME )>:
5330					The primary (unique) key name.
5331
5332					B<DEFERRABILITY ( DEFERABILITY )>:
5333					The deferrability of the foreign key constraint.
5334					The following codes are defined:
5335
5336					INITIALLY DEFERRED 5
5337					INITIALLY IMMEDIATE 6
5338					NOT DEFERRABLE 7
5339
5340					B< ( UNIQUE_OR_PRIMARY )>:
5341					This column is necessary if a driver includes all candidate (i.e. primary and
5342					alternate) keys in the result set (as specified by SQL/CLI).
5343					The value of this column is UNIQUE if the foreign key references an alternate
5344					key and PRIMARY if the foreign key references a primary key, or it
5345					may be undefined if the driver doesn't have access to the information.
5346
5347					See also L</"Catalog Methods"> and L</"Standards Reference Information">.
5348
5349					=head3 C<statistics_info>
5350
5351					B<Warning:> This method is experimental and may change.
5352
5353					$sth = $dbh->statistics_info( $catalog, $schema, $table, $unique_only, $quick );
5354
5355					# then $sth->fetchall_arrayref or $sth->fetchall_hashref etc
5356
5357					Returns an active statement handle that can be used to fetch statistical
5358					information about a table and its indexes.
5359
5360					The arguments don't accept search patterns (unlike L</table_info>).
5361
5362					If the boolean argument $unique_only is true, only UNIQUE indexes will be
5363					returned in the result set, otherwise all indexes will be returned.
5364
5365					If the boolean argument $quick is set, the actual statistical information
5366					columns (CARDINALITY and PAGES) will only be returned if they are readily
5367					available from the server, and might not be current. Some databases may
5368					return stale statistics or no statistics at all with this flag set.
5369
5370					The statement handle will return at most one row per column name per index,
5371					plus at most one row for the entire table itself, ordered by NON_UNIQUE, TYPE,
5372					INDEX_QUALIFIER, INDEX_NAME, and ORDINAL_POSITION.
5373
5374					Note: The support for the selection criteria, such as $catalog, is
5375					driver specific. If the driver doesn't support catalogs and/or
5376					schemas, it may ignore these criteria.
5377
5378					The statement handle returned has at least the following fields in the
5379					order shown below. Other fields, after these, may also be present.
5380
5381					B<TABLE_CAT>: The catalog identifier.
5382					This field is NULL (C<undef>) if not applicable to the data source,
5383					which is often the case. This field is empty if not applicable to the
5384					table.
5385
5386					B<TABLE_SCHEM>: The schema identifier.
5387					This field is NULL (C<undef>) if not applicable to the data source,
5388					and empty if not applicable to the table.
5389
5390					B<TABLE_NAME>: The table identifier.
5391
5392					B<NON_UNIQUE>: Unique index indicator.
5393					Returns 0 for unique indexes, 1 for non-unique indexes
5394
5395					B<INDEX_QUALIFIER>: Index qualifier identifier.
5396					The identifier that is used to qualify the index name when doing a
5397					C<DROP INDEX>; NULL (C<undef>) is returned if an index qualifier is not
5398					supported by the data source.
5399					If a non-NULL (defined) value is returned in this column, it must be used
5400					to qualify the index name on a C<DROP INDEX> statement; otherwise,
5401					the TABLE_SCHEM should be used to qualify the index name.
5402
5403					B<INDEX_NAME>: The index identifier.
5404
5405					B<TYPE>: The type of information being returned. Can be any of the
5406					following values: 'table', 'btree', 'clustered', 'content', 'hashed',
5407					or 'other'.
5408
5409					In the case that this field is 'table', all fields
5410					other than TABLE_CAT, TABLE_SCHEM, TABLE_NAME, TYPE,
5411					CARDINALITY, and PAGES will be NULL (C<undef>).
5412
5413					B<ORDINAL_POSITION>: Column sequence number (starting with 1).
5414
5415					B<COLUMN_NAME>: The column identifier.
5416
5417					B<ASC_OR_DESC>: Column sort sequence.
5418					C<A> for Ascending, C<D> for Descending, or NULL (C<undef>) if
5419					not supported for this index.
5420
5421					B<CARDINALITY>: Cardinality of the table or index.
5422					For indexes, this is the number of unique values in the index.
5423					For tables, this is the number of rows in the table.
5424					If not supported, the value will be NULL (C<undef>).
5425
5426					B<PAGES>: Number of storage pages used by this table or index.
5427					If not supported, the value will be NULL (C<undef>).
5428
5429					B<FILTER_CONDITION>: The index filter condition as a string.
5430					If the index is not a filtered index, or it cannot be determined
5431					whether the index is a filtered index, this value is NULL (C<undef>).
5432					If the index is a filtered index, but the filter condition
5433					cannot be determined, this value is the empty string C<''>.
5434					Otherwise it will be the literal filter condition as a string,
5435					such as C<SALARY <= 4500>.
5436
5437					See also L</"Catalog Methods"> and L</"Standards Reference Information">.
5438
5439					=head3 C<tables>
5440
5441					@names = $dbh->tables( $catalog, $schema, $table, $type );
5442					@names = $dbh->tables; # deprecated
5443
5444					Simple interface to table_info(). Returns a list of matching
5445					table names, possibly including a catalog/schema prefix.
5446
5447					See L</table_info> for a description of the parameters.
5448
5449					If C<$dbh-E<gt>get_info(29)> returns true (29 is SQL_IDENTIFIER_QUOTE_CHAR)
5450					then the table names are constructed and quoted by L</quote_identifier>
5451					to ensure they are usable even if they contain whitespace or reserved
5452					words etc. This means that the table names returned will include
5453					quote characters.
5454
5455					=head3 C<type_info_all>
5456
5457					$type_info_all = $dbh->type_info_all;
5458
5459					Returns a reference to an array which holds information about each data
5460					type variant supported by the database and driver. The array and its
5461					contents should be treated as read-only.
5462
5463					The first item is a reference to an 'index' hash of C<Name =>E<gt> C<Index> pairs.
5464					The items following that are references to arrays, one per supported data
5465					type variant. The leading index hash defines the names and order of the
5466					fields within the arrays that follow it.
5467					For example:
5468
5469					$type_info_all = [
5470					{ TYPE_NAME => 0,
5471					DATA_TYPE => 1,
5472					COLUMN_SIZE => 2, # was PRECISION originally
5473					LITERAL_PREFIX => 3,
5474					LITERAL_SUFFIX => 4,
5475					CREATE_PARAMS => 5,
5476					NULLABLE => 6,
5477					CASE_SENSITIVE => 7,
5478					SEARCHABLE => 8,
5479					UNSIGNED_ATTRIBUTE=> 9,
5480					FIXED_PREC_SCALE => 10, # was MONEY originally
5481					AUTO_UNIQUE_VALUE => 11, # was AUTO_INCREMENT originally
5482					LOCAL_TYPE_NAME => 12,
5483					MINIMUM_SCALE => 13,
5484					MAXIMUM_SCALE => 14,
5485					SQL_DATA_TYPE => 15,
5486					SQL_DATETIME_SUB => 16,
5487					NUM_PREC_RADIX => 17,
5488					INTERVAL_PRECISION=> 18,
5489					},
5490					[ 'VARCHAR', SQL_VARCHAR,
5491					undef, "'","'", undef,0, 1,1,0,0,0,undef,1,255, undef
5492					],
5493					[ 'INTEGER', SQL_INTEGER,
5494					undef, "", "", undef,0, 0,1,0,0,0,undef,0, 0, 10
5495					],
5496					];
5497
5498					More than one row may have the same value in the C<DATA_TYPE>
5499					field if there are different ways to spell the type name and/or there
5500					are variants of the type with different attributes (e.g., with and
5501					without C<AUTO_UNIQUE_VALUE> set, with and without C<UNSIGNED_ATTRIBUTE>, etc).
5502
5503					The rows are ordered by C<DATA_TYPE> first and then by how closely each
5504					type maps to the corresponding ODBC SQL data type, closest first.
5505
5506					The meaning of the fields is described in the documentation for
5507					the L</type_info> method.
5508
5509					An 'index' hash is provided so you don't need to rely on index
5510					values defined above. However, using DBD::ODBC with some old ODBC
5511					drivers may return older names, shown as comments in the example above.
5512					Another issue with the index hash is that the lettercase of the
5513					keys is not defined. It is usually uppercase, as show here, but
5514					drivers may return names with any lettercase.
5515
5516					Drivers are also free to return extra driver-specific columns of
5517					information - though it's recommended that they start at column
5518					index 50 to leave room for expansion of the DBI/ODBC specification.
5519
5520					The type_info_all() method is not normally used directly.
5521					The L</type_info> method provides a more usable and useful interface
5522					to the data.
5523
5524					=head3 C<type_info>
5525
5526					@type_info = $dbh->type_info($data_type);
5527
5528					Returns a list of hash references holding information about one or more
5529					variants of $data_type. The list is ordered by C<DATA_TYPE> first and
5530					then by how closely each type maps to the corresponding ODBC SQL data
5531					type, closest first. If called in a scalar context then only the first
5532					(best) element is returned.
5533
5534					If $data_type is undefined or C<SQL_ALL_TYPES>, then the list will
5535					contain hashes for all data type variants supported by the database and driver.
5536
5537					If $data_type is an array reference then C<type_info> returns the
5538					information for the I<first> type in the array that has any matches.
5539
5540					The keys of the hash follow the same letter case conventions as the
5541					rest of the DBI (see L</Naming Conventions and Name Space>). The
5542					following uppercase items should always exist, though may be undef:
5543
5544					=over 4
5545
5546					=item TYPE_NAME (string)
5547
5548					Data type name for use in CREATE TABLE statements etc.
5549
5550					=item DATA_TYPE (integer)
5551
5552					SQL data type number.
5553
5554					=item COLUMN_SIZE (integer)
5555
5556					For numeric types, this is either the total number of digits (if the
5557					NUM_PREC_RADIX value is 10) or the total number of bits allowed in the
5558					column (if NUM_PREC_RADIX is 2).
5559
5560					For string types, this is the maximum size of the string in characters.
5561
5562					For date and interval types, this is the maximum number of characters
5563					needed to display the value.
5564
5565					=item LITERAL_PREFIX (string)
5566
5567					Characters used to prefix a literal. A typical prefix is "C<'>" for characters,
5568					or possibly "C<0x>" for binary values passed as hexadecimal. NULL (C<undef>) is
5569					returned for data types for which this is not applicable.
5570
5571
5572					=item LITERAL_SUFFIX (string)
5573
5574					Characters used to suffix a literal. Typically "C<'>" for characters.
5575					NULL (C<undef>) is returned for data types where this is not applicable.
5576
5577					=item CREATE_PARAMS (string)
5578
5579					Parameter names for data type definition. For example, C<CREATE_PARAMS> for a
5580					C<DECIMAL> would be "C<precision,scale>" if the DECIMAL type should be
5581					declared as C<DECIMAL(>I<precision,scale>C<)> where I<precision> and I<scale>
5582					are integer values. For a C<VARCHAR> it would be "C<max length>".
5583					NULL (C<undef>) is returned for data types for which this is not applicable.
5584
5585					=item NULLABLE (integer)
5586
5587					Indicates whether the data type accepts a NULL value:
5588					C<0> or an empty string = no, C<1> = yes, C<2> = unknown.
5589
5590					=item CASE_SENSITIVE (boolean)
5591
5592					Indicates whether the data type is case sensitive in collations and
5593					comparisons.
5594
5595					=item SEARCHABLE (integer)
5596
5597					Indicates how the data type can be used in a WHERE clause, as
5598					follows:
5599
5600					0 - Cannot be used in a WHERE clause
5601					1 - Only with a LIKE predicate
5602					2 - All comparison operators except LIKE
5603					3 - Can be used in a WHERE clause with any comparison operator
5604
5605					=item UNSIGNED_ATTRIBUTE (boolean)
5606
5607					Indicates whether the data type is unsigned. NULL (C<undef>) is returned
5608					for data types for which this is not applicable.
5609
5610					=item FIXED_PREC_SCALE (boolean)
5611
5612					Indicates whether the data type always has the same precision and scale
5613					(such as a money type). NULL (C<undef>) is returned for data types
5614					for which
5615					this is not applicable.
5616
5617					=item AUTO_UNIQUE_VALUE (boolean)
5618
5619					Indicates whether a column of this data type is automatically set to a
5620					unique value whenever a new row is inserted. NULL (C<undef>) is returned
5621					for data types for which this is not applicable.
5622
5623					=item LOCAL_TYPE_NAME (string)
5624
5625					Localized version of the C<TYPE_NAME> for use in dialog with users.
5626					NULL (C<undef>) is returned if a localized name is not available (in which
5627					case C<TYPE_NAME> should be used).
5628
5629					=item MINIMUM_SCALE (integer)
5630
5631					The minimum scale of the data type. If a data type has a fixed scale,
5632					then C<MAXIMUM_SCALE> holds the same value. NULL (C<undef>) is returned for
5633					data types for which this is not applicable.
5634
5635					=item MAXIMUM_SCALE (integer)
5636
5637					The maximum scale of the data type. If a data type has a fixed scale,
5638					then C<MINIMUM_SCALE> holds the same value. NULL (C<undef>) is returned for
5639					data types for which this is not applicable.
5640
5641					=item SQL_DATA_TYPE (integer)
5642
5643					This column is the same as the C<DATA_TYPE> column, except for interval
5644					and datetime data types. For interval and datetime data types, the
5645					C<SQL_DATA_TYPE> field will return C<SQL_INTERVAL> or C<SQL_DATETIME>, and the
5646					C<SQL_DATETIME_SUB> field below will return the subcode for the specific
5647					interval or datetime data type. If this field is NULL, then the driver
5648					does not support or report on interval or datetime subtypes.
5649
5650					=item SQL_DATETIME_SUB (integer)
5651
5652					For interval or datetime data types, where the C<SQL_DATA_TYPE>
5653					field above is C<SQL_INTERVAL> or C<SQL_DATETIME>, this field will
5654					hold the I<subcode> for the specific interval or datetime data type.
5655					Otherwise it will be NULL (C<undef>).
5656
5657					Although not mentioned explicitly in the standards, it seems there
5658					is a simple relationship between these values:
5659
5660					DATA_TYPE == (10 * SQL_DATA_TYPE) + SQL_DATETIME_SUB
5661
5662					=item NUM_PREC_RADIX (integer)
5663
5664					The radix value of the data type. For approximate numeric types,
5665					C<NUM_PREC_RADIX>
5666					contains the value 2 and C<COLUMN_SIZE> holds the number of bits. For
5667					exact numeric types, C<NUM_PREC_RADIX> contains the value 10 and C<COLUMN_SIZE> holds
5668					the number of decimal digits. NULL (C<undef>) is returned either for data types
5669					for which this is not applicable or if the driver cannot report this information.
5670
5671					=item INTERVAL_PRECISION (integer)
5672
5673					The interval leading precision for interval types. NULL is returned
5674					either for data types for which this is not applicable or if the driver
5675					cannot report this information.
5676
5677					=back
5678
5679					For example, to find the type name for the fields in a select statement
5680					you can do:
5681
5682					@names = map { scalar $dbh->type_info($_)->{TYPE_NAME} } @{ $sth->{TYPE} }
5683
5684					Since DBI and ODBC drivers vary in how they map their types into the
5685					ISO standard types you may need to search for more than one type.
5686					Here's an example looking for a usable type to store a date:
5687
5688					$my_date_type = $dbh->type_info( [ SQL_DATE, SQL_TIMESTAMP ] );
5689
5690					Similarly, to more reliably find a type to store small integers, you could
5691					use a list starting with C<SQL_SMALLINT>, C<SQL_INTEGER>, C<SQL_DECIMAL>, etc.
5692
5693					See also L</"Standards Reference Information">.
5694
5695
5696					=head3 C<quote>
5697
5698					$sql = $dbh->quote($value);
5699					$sql = $dbh->quote($value, $data_type);
5700
5701					Quote a string literal for use as a literal value in an SQL statement,
5702					by escaping any special characters (such as quotation marks)
5703					contained within the string and adding the required type of outer
5704					quotation marks.
5705
5706					$sql = sprintf "SELECT foo FROM bar WHERE baz = %s",
5707					$dbh->quote("Don't");
5708
5709					For most database types, at least those that conform to SQL standards, quote
5710					would return C<'Don''t'> (including the outer quotation marks). For others it
5711					may return something like C<'Don\'t'>
5712
5713					An undefined C<$value> value will be returned as the string C<NULL> (without
5714					single quotation marks) to match how NULLs are represented in SQL.
5715
5716					If C<$data_type> is supplied, it is used to try to determine the required
5717					quoting behaviour by using the information returned by L</type_info>.
5718					As a special case, the standard numeric types are optimized to return
5719					C<$value> without calling C<type_info>.
5720
5721					Quote will probably I<not> be able to deal with all possible input
5722					(such as binary data or data containing newlines), and is not related in
5723					any way with escaping or quoting shell meta-characters.
5724
5725					It is valid for the quote() method to return an SQL expression that
5726					evaluates to the desired string. For example:
5727
5728					$quoted = $dbh->quote("one\ntwo\0three")
5729
5730					may return something like:
5731
5732					CONCAT('one', CHAR(12), 'two', CHAR(0), 'three')
5733
5734					The quote() method should I<not> be used with L</"Placeholders and
5735					Bind Values">.
5736
5737					=head3 C<quote_identifier>
5738
5739					$sql = $dbh->quote_identifier( $name );
5740					$sql = $dbh->quote_identifier( $catalog, $schema, $table, \%attr );
5741
5742					Quote an identifier (table name etc.) for use in an SQL statement,
5743					by escaping any special characters (such as double quotation marks)
5744					it contains and adding the required type of outer quotation marks.
5745
5746					Undefined names are ignored and the remainder are quoted and then
5747					joined together, typically with a dot (C<.>) character. For example:
5748
5749					$id = $dbh->quote_identifier( undef, 'Her schema', 'My table' );
5750
5751					would, for most database types, return C<"Her schema"."My table">
5752					(including all the double quotation marks).
5753
5754					If three names are supplied then the first is assumed to be a
5755					catalog name and special rules may be applied based on what L</get_info>
5756					returns for SQL_CATALOG_NAME_SEPARATOR (41) and SQL_CATALOG_LOCATION (114).
5757					For example, for Oracle:
5758
5759					$id = $dbh->quote_identifier( 'link', 'schema', 'table' );
5760
5761					would return C<"schema"."table"@"link">.
5762
5763					=head3 C<take_imp_data>
5764
5765					$imp_data = $dbh->take_imp_data;
5766
5767					Leaves the $dbh in an almost dead, zombie-like, state and returns
5768					a binary string of raw implementation data from the driver which
5769					describes the current database connection. Effectively it detaches
5770					the underlying database API connection data from the DBI handle.
5771					After calling take_imp_data(), all other methods except C<DESTROY>
5772					will generate a warning and return undef.
5773
5774					Why would you want to do this? You don't, forget I even mentioned it.
5775					Unless, that is, you're implementing something advanced like a
5776					multi-threaded connection pool. See L<DBI::Pool>.
5777
5778					The returned $imp_data can be passed as a C<dbi_imp_data> attribute
5779					to a later connect() call, even in a separate thread in the same
5780					process, where the driver can use it to 'adopt' the existing
5781					connection that the implementation data was taken from.
5782
5783					Some things to keep in mind...
5784
5785					B<*> the $imp_data holds the only reference to the underlying
5786					database API connection data. That connection is still 'live' and
5787					won't be cleaned up properly unless the $imp_data is used to create
5788					a new $dbh which is then allowed to disconnect() normally.
5789
5790					B<*> using the same $imp_data to create more than one other new
5791					$dbh at a time may well lead to unpleasant problems. Don't do that.
5792
5793					Any child statement handles are effectively destroyed when take_imp_data() is
5794					called.
5795
5796					The C<take_imp_data> method was added in DBI 1.36 but wasn't useful till 1.49.
5797
5798
5799					=head2 Database Handle Attributes
5800
5801					This section describes attributes specific to database handles.
5802
5803					Changes to these database handle attributes do not affect any other
5804					existing or future database handles.
5805
5806					Attempting to set or get the value of an unknown attribute generates a warning,
5807					except for private driver-specific attributes (which all have names
5808					starting with a lowercase letter).
5809
5810					Example:
5811
5812					$h->{AutoCommit} = ...; # set/write
5813					... = $h->{AutoCommit}; # get/read
5814
5815					=head3 C<AutoCommit>
5816
5817					Type: boolean
5818
5819					If true, then database changes cannot be rolled-back (undone). If false,
5820					then database changes automatically occur within a "transaction", which
5821					must either be committed or rolled back using the C<commit> or C<rollback>
5822					methods.
5823
5824					Drivers should always default to C<AutoCommit> mode (an unfortunate
5825					choice largely forced on the DBI by ODBC and JDBC conventions.)
5826
5827					Attempting to set C<AutoCommit> to an unsupported value is a fatal error.
5828					This is an important feature of the DBI. Applications that need
5829					full transaction behaviour can set C<$dbh-E<gt>{AutoCommit} = 0> (or
5830					set C<AutoCommit> to 0 via L</connect>)
5831					without having to check that the value was assigned successfully.
5832
5833					For the purposes of this description, we can divide databases into three
5834					categories:
5835
5836					Databases which don't support transactions at all.
5837					Databases in which a transaction is always active.
5838					Databases in which a transaction must be explicitly started (C<'BEGIN WORK'>).
5839
5840					B<* Databases which don't support transactions at all>
5841
5842					For these databases, attempting to turn C<AutoCommit> off is a fatal error.
5843					C<commit> and C<rollback> both issue warnings about being ineffective while
5844					C<AutoCommit> is in effect.
5845
5846					B<* Databases in which a transaction is always active>
5847
5848					These are typically mainstream commercial relational databases with
5849					"ANSI standard" transaction behaviour.
5850					If C<AutoCommit> is off, then changes to the database won't have any
5851					lasting effect unless L</commit> is called (but see also
5852					L</disconnect>). If L</rollback> is called then any changes since the
5853					last commit are undone.
5854
5855					If C<AutoCommit> is on, then the effect is the same as if the DBI
5856					called C<commit> automatically after every successful database
5857					operation. So calling C<commit> or C<rollback> explicitly while
5858					C<AutoCommit> is on would be ineffective because the changes would
5859					have already been committed.
5860
5861					Changing C<AutoCommit> from off to on will trigger a L</commit>.
5862
5863					For databases which don't support a specific auto-commit mode, the
5864					driver has to commit each statement automatically using an explicit
5865					C<COMMIT> after it completes successfully (and roll it back using an
5866					explicit C<ROLLBACK> if it fails). The error information reported to the
5867					application will correspond to the statement which was executed, unless
5868					it succeeded and the commit or rollback failed.
5869
5870					B<* Databases in which a transaction must be explicitly started>
5871
5872					For these databases, the intention is to have them act like databases in
5873					which a transaction is always active (as described above).
5874
5875					To do this, the driver will automatically begin an explicit transaction
5876					when C<AutoCommit> is turned off, or after a L</commit> or
5877					L</rollback> (or when the application issues the next database
5878					operation after one of those events).
5879
5880					In this way, the application does not have to treat these databases
5881					as a special case.
5882
5883					See L</commit>, L</disconnect> and L</Transactions> for other important
5884					notes about transactions.
5885
5886
5887					=head3 C<Driver>
5888
5889					Type: handle
5890
5891					Holds the handle of the parent driver. The only recommended use for this
5892					is to find the name of the driver using:
5893
5894					$dbh->{Driver}->{Name}
5895
5896
5897					=head3 C<Name>
5898
5899					Type: string
5900
5901					Holds the "name" of the database. Usually (and recommended to be) the
5902					same as the "C<dbi:DriverName:...>" string used to connect to the database,
5903					but with the leading "C<dbi:DriverName:>" removed.
5904
5905
5906					=head3 C<Statement>
5907
5908					Type: string, read-only
5909
5910					Returns the statement string passed to the most recent L</prepare> or
5911					L</do> method called in this database handle, even if that method
5912					failed. This is especially useful where C<RaiseError> is enabled and
5913					the exception handler checks $@ and sees that a 'prepare' method call
5914					failed.
5915
5916
5917					=head3 C<RowCacheSize>
5918
5919					Type: integer
5920
5921					A hint to the driver indicating the size of the local row cache that the
5922					application would like the driver to use for future C<SELECT> statements.
5923					If a row cache is not implemented, then setting C<RowCacheSize> is ignored
5924					and getting the value returns C<undef>.
5925
5926					Some C<RowCacheSize> values have special meaning, as follows:
5927
5928					0 - Automatically determine a reasonable cache size for each C<SELECT>
5929					1 - Disable the local row cache
5930					>1 - Cache this many rows
5931					<0 - Cache as many rows that will fit into this much memory for each C<SELECT>.
5932
5933					Note that large cache sizes may require a very large amount of memory
5934					(I<cached rows * maximum size of row>). Also, a large cache will cause
5935					a longer delay not only for the first fetch, but also whenever the
5936					cache needs refilling.
5937
5938					See also the L</RowsInCache> statement handle attribute.
5939
5940					=head3 C<Username>
5941
5942					Type: string
5943
5944					Returns the username used to connect to the database.
5945
5946
5947					=head1 DBI STATEMENT HANDLE OBJECTS
5948
5949					This section lists the methods and attributes associated with DBI
5950					statement handles.
5951
5952					=head2 Statement Handle Methods
5953
5954					The DBI defines the following methods for use on DBI statement handles:
5955
5956					=head3 C<bind_param>
5957
5958					$sth->bind_param($p_num, $bind_value)
5959					$sth->bind_param($p_num, $bind_value, \%attr)
5960					$sth->bind_param($p_num, $bind_value, $bind_type)
5961
5962					The C<bind_param> method takes a copy of $bind_value and associates it
5963					(binds it) with a placeholder, identified by $p_num, embedded in
5964					the prepared statement. Placeholders are indicated with question
5965					mark character (C<?>). For example:
5966
5967					$dbh->{RaiseError} = 1; # save having to check each method call
5968					$sth = $dbh->prepare("SELECT name, age FROM people WHERE name LIKE ?");
5969					$sth->bind_param(1, "John%"); # placeholders are numbered from 1
5970					$sth->execute;
5971					DBI::dump_results($sth);
5972
5973					See L</"Placeholders and Bind Values"> for more information.
5974
5975
5976					B<Data Types for Placeholders>
5977
5978					The C<\%attr> parameter can be used to hint at the data type the
5979					placeholder should have. This is rarely needed. Typically, the driver is only
5980					interested in knowing if the placeholder should be bound as a number or a string.
5981
5982					$sth->bind_param(1, $value, { TYPE => SQL_INTEGER });
5983
5984					As a short-cut for the common case, the data type can be passed
5985					directly, in place of the C<\%attr> hash reference. This example is
5986					equivalent to the one above:
5987
5988					$sth->bind_param(1, $value, SQL_INTEGER);
5989
5990					The C<TYPE> value indicates the standard (non-driver-specific) type for
5991					this parameter. To specify the driver-specific type, the driver may
5992					support a driver-specific attribute, such as C<{ ora_type =E<gt> 97 }>.
5993
5994					The SQL_INTEGER and other related constants can be imported using
5995
5996					use DBI qw(:sql_types);
5997
5998					See L</"DBI Constants"> for more information.
5999
6000					The data type is 'sticky' in that bind values passed to execute() are bound
6001					with the data type specified by earlier bind_param() calls, if any.
6002					Portable applications should not rely on being able to change the data type
6003					after the first C<bind_param> call.
6004
6005					Perl only has string and number scalar data types. All database types
6006					that aren't numbers are bound as strings and must be in a format the
6007					database will understand except where the bind_param() TYPE attribute
6008					specifies a type that implies a particular format. For example, given:
6009
6010					$sth->bind_param(1, $value, SQL_DATETIME);
6011
6012					the driver should expect $value to be in the ODBC standard SQL_DATETIME
6013					format, which is 'YYYY-MM-DD HH:MM:SS'. Similarly for SQL_DATE, SQL_TIME etc.
6014
6015					As an alternative to specifying the data type in the C<bind_param> call,
6016					you can let the driver pass the value as the default type (C<VARCHAR>).
6017					You can then use an SQL function to convert the type within the statement.
6018					For example:
6019
6020					INSERT INTO price(code, price) VALUES (?, CONVERT(MONEY,?))
6021
6022					The C<CONVERT> function used here is just an example. The actual function
6023					and syntax will vary between different databases and is non-portable.
6024
6025					See also L</"Placeholders and Bind Values"> for more information.
6026
6027
6028					=head3 C<bind_param_inout>
6029
6030					$rc = $sth->bind_param_inout($p_num, \$bind_value, $max_len) or die $sth->errstr;
6031					$rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, \%attr) or ...
6032					$rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, $bind_type) or ...
6033
6034					This method acts like L</bind_param>, but also enables values to be
6035					updated by the statement. The statement is typically
6036					a call to a stored procedure. The C<$bind_value> must be passed as a
6037					reference to the actual value to be used.
6038
6039					Note that unlike L</bind_param>, the C<$bind_value> variable is not
6040					copied when C<bind_param_inout> is called. Instead, the value in the
6041					variable is read at the time L</execute> is called.
6042
6043					The additional C<$max_len> parameter specifies the minimum amount of
6044					memory to allocate to C<$bind_value> for the new value. If the value
6045					returned from the database is too
6046					big to fit, then the execution should fail. If unsure what value to use,
6047					pick a generous length, i.e., a length larger than the longest value that would ever be
6048					returned. The only cost of using a larger value than needed is wasted memory.
6049
6050					Undefined values or C<undef> are used to indicate null values.
6051					See also L</"Placeholders and Bind Values"> for more information.
6052
6053
6054					=head3 C<bind_param_array>
6055
6056					$rc = $sth->bind_param_array($p_num, $array_ref_or_value)
6057					$rc = $sth->bind_param_array($p_num, $array_ref_or_value, \%attr)
6058					$rc = $sth->bind_param_array($p_num, $array_ref_or_value, $bind_type)
6059
6060					The C<bind_param_array> method is used to bind an array of values
6061					to a placeholder embedded in the prepared statement which is to be executed
6062					with L</execute_array>. For example:
6063
6064					$dbh->{RaiseError} = 1; # save having to check each method call
6065					$sth = $dbh->prepare("INSERT INTO staff (first_name, last_name, dept) VALUES(?, ?, ?)");
6066					$sth->bind_param_array(1, [ 'John', 'Mary', 'Tim' ]);
6067					$sth->bind_param_array(2, [ 'Booth', 'Todd', 'Robinson' ]);
6068					$sth->bind_param_array(3, "SALES"); # scalar will be reused for each row
6069					$sth->execute_array( { ArrayTupleStatus => \my @tuple_status } );
6070
6071					The C<%attr> ($bind_type) argument is the same as defined for L</bind_param>.
6072					Refer to L</bind_param> for general details on using placeholders.
6073
6074					(Note that bind_param_array() can I<not> be used to expand a
6075					placeholder into a list of values for a statement like "SELECT foo
6076					WHERE bar IN (?)". A placeholder can only ever represent one value
6077					per execution.)
6078
6079					Scalar values, including C<undef>, may also be bound by
6080					C<bind_param_array>. In which case the same value will be used for each
6081					L</execute> call. Driver-specific implementations may behave
6082					differently, e.g., when binding to a stored procedure call, some
6083					databases may permit mixing scalars and arrays as arguments.
6084
6085					The default implementation provided by DBI (for drivers that have
6086					not implemented array binding) is to iteratively call L</execute> for
6087					each parameter tuple provided in the bound arrays. Drivers may
6088					provide more optimized implementations using whatever bulk operation
6089					support the database API provides. The default driver behaviour should
6090					match the default DBI behaviour, but always consult your driver
6091					documentation as there may be driver specific issues to consider.
6092
6093					Note that the default implementation currently only supports non-data
6094					returning statements (INSERT, UPDATE, but not SELECT). Also,
6095					C<bind_param_array> and L</bind_param> cannot be mixed in the same
6096					statement execution, and C<bind_param_array> must be used with
6097					L</execute_array>; using C<bind_param_array> will have no effect
6098					for L</execute>.
6099
6100					The C<bind_param_array> method was added in DBI 1.22.
6101
6102					=head3 C<execute>
6103
6104					$rv = $sth->execute or die $sth->errstr;
6105					$rv = $sth->execute(@bind_values) or die $sth->errstr;
6106
6107					Perform whatever processing is necessary to execute the prepared
6108					statement. An C<undef> is returned if an error occurs. A successful
6109					C<execute> always returns true regardless of the number of rows affected,
6110					even if it's zero (see below). It is always important to check the
6111					return status of C<execute> (and most other DBI methods) for errors
6112					if you're not using L</RaiseError>.
6113
6114					For a I<non>-C<SELECT> statement, C<execute> returns the number of rows
6115					affected, if known. If no rows were affected, then C<execute> returns
6116					"C<0E0>", which Perl will treat as 0 but will regard as true. Note that it
6117					is I<not> an error for no rows to be affected by a statement. If the
6118					number of rows affected is not known, then C<execute> returns -1.
6119
6120					For C<SELECT> statements, execute simply "starts" the query within the
6121					database engine. Use one of the fetch methods to retrieve the data after
6122					calling C<execute>. The C<execute> method does I<not> return the number of
6123					rows that will be returned by the query (because most databases can't
6124					tell in advance), it simply returns a true value.
6125
6126					You can tell if the statement was a C<SELECT> statement by checking if
6127					C<$sth-E<gt>{NUM_OF_FIELDS}> is greater than zero after calling C<execute>.
6128
6129					If any arguments are given, then C<execute> will effectively call
6130					L</bind_param> for each value before executing the statement. Values
6131					bound in this way are usually treated as C<SQL_VARCHAR> types unless
6132					the driver can determine the correct type (which is rare), or unless
6133					C<bind_param> (or C<bind_param_inout>) has already been used to
6134					specify the type.
6135
6136					Note that passing C<execute> an empty array is the same as passing no arguments
6137					at all, which will execute the statement with previously bound values.
6138					That's probably not what you want.
6139
6140					If execute() is called on a statement handle that's still active
6141					($sth->{Active} is true) then it should effectively call finish()
6142					to tidy up the previous execution results before starting this new
6143					execution.
6144
6145					=head3 C<execute_array>
6146
6147					$tuples = $sth->execute_array(\%attr) or die $sth->errstr;
6148					$tuples = $sth->execute_array(\%attr, @bind_values) or die $sth->errstr;
6149
6150					($tuples, $rows) = $sth->execute_array(\%attr) or die $sth->errstr;
6151					($tuples, $rows) = $sth->execute_array(\%attr, @bind_values) or die $sth->errstr;
6152
6153					Execute the prepared statement once for each parameter tuple
6154					(group of values) provided either in the @bind_values, or by prior
6155					calls to L</bind_param_array>, or via a reference passed in \%attr.
6156
6157					When called in scalar context the execute_array() method returns the
6158					number of tuples executed, or C<undef> if an error occurred. Like
6159					execute(), a successful execute_array() always returns true regardless
6160					of the number of tuples executed, even if it's zero. If there were any
6161					errors the ArrayTupleStatus array can be used to discover which tuples
6162					failed and with what errors.
6163
6164					When called in list context the execute_array() method returns two scalars;
6165					$tuples is the same as calling execute_array() in scalar context and $rows is
6166					the number of rows affected for each tuple, if available or
6167					-1 if the driver cannot determine this. NOTE, some drivers cannot determine
6168					the number of rows affected per tuple but can provide the number of rows
6169					affected for the batch.
6170					If you are doing an update operation the returned rows affected may not be what
6171					you expect if, for instance, one or more of the tuples affected the same row
6172					multiple times. Some drivers may not yet support list context, in which case
6173					$rows will be undef, or may not be able to provide the number of rows affected
6174					when performing this batch operation, in which case $rows will be -1.
6175
6176					Bind values for the tuples to be executed may be supplied row-wise
6177					by an C<ArrayTupleFetch> attribute, or else column-wise in the
6178					C<@bind_values> argument, or else column-wise by prior calls to
6179					L</bind_param_array>.
6180
6181					Where column-wise binding is used (via the C<@bind_values> argument
6182					or calls to bind_param_array()) the maximum number of elements in
6183					any one of the bound value arrays determines the number of tuples
6184					executed. Placeholders with fewer values in their parameter arrays
6185					are treated as if padded with undef (NULL) values.
6186
6187					If a scalar value is bound, instead of an array reference, it is
6188					treated as a I<variable> length array with all elements having the
6189					same value. It does not influence the number of tuples executed,
6190					so if all bound arrays have zero elements then zero tuples will
6191					be executed. If I<all> bound values are scalars then one tuple
6192					will be executed, making execute_array() act just like execute().
6193
6194					The C<ArrayTupleFetch> attribute can be used to specify a reference
6195					to a subroutine that will be called to provide the bind values for
6196					each tuple execution. The subroutine should return an reference to
6197					an array which contains the appropriate number of bind values, or
6198					return an undef if there is no more data to execute.
6199
6200					As a convenience, the C<ArrayTupleFetch> attribute can also be
6201					used to specify a statement handle. In which case the fetchrow_arrayref()
6202					method will be called on the given statement handle in order to
6203					provide the bind values for each tuple execution.
6204
6205					The values specified via bind_param_array() or the @bind_values
6206					parameter may be either scalars, or arrayrefs. If any C<@bind_values>
6207					are given, then C<execute_array> will effectively call L</bind_param_array>
6208					for each value before executing the statement. Values bound in
6209					this way are usually treated as C<SQL_VARCHAR> types unless the
6210					driver can determine the correct type (which is rare), or unless
6211					C<bind_param>, C<bind_param_inout>, C<bind_param_array>, or
6212					C<bind_param_inout_array> has already been used to specify the type.
6213					See L</bind_param_array> for details.
6214
6215					The C<ArrayTupleStatus> attribute can be used to specify a
6216					reference to an array which will receive the execute status of each
6217					executed parameter tuple. Note the C<ArrayTupleStatus> attribute was
6218					mandatory until DBI 1.38.
6219
6220					For tuples which are successfully executed, the element at the same
6221					ordinal position in the status array is the resulting rowcount (or -1
6222					if unknown).
6223					If the execution of a tuple causes an error, then the corresponding
6224					status array element will be set to a reference to an array containing
6225					L</err>, L</errstr> and L</state> set by the failed execution.
6226
6227					If B<any> tuple execution returns an error, C<execute_array> will
6228					return C<undef>. In that case, the application should inspect the
6229					status array to determine which parameter tuples failed.
6230					Some databases may not continue executing tuples beyond the first
6231					failure. In this case the status array will either hold fewer
6232					elements, or the elements beyond the failure will be undef.
6233
6234					If all parameter tuples are successfully executed, C<execute_array>
6235					returns the number tuples executed. If no tuples were executed,
6236					then execute_array() returns "C<0E0>", just like execute() does,
6237					which Perl will treat as 0 but will regard as true.
6238
6239					For example:
6240
6241					$sth = $dbh->prepare("INSERT INTO staff (first_name, last_name) VALUES (?, ?)");
6242					my $tuples = $sth->execute_array(
6243					{ ArrayTupleStatus => \my @tuple_status },
6244					\@first_names,
6245					\@last_names,
6246					);
6247					if ($tuples) {
6248					print "Successfully inserted $tuples records\n";
6249					}
6250					else {
6251					for my $tuple (0..@last_names-1) {
6252					my $status = $tuple_status[$tuple];
6253					$status = [0, "Skipped"] unless defined $status;
6254					next unless ref $status;
6255					printf "Failed to insert (%s, %s): %s\n",
6256					$first_names[$tuple], $last_names[$tuple], $status->[1];
6257					}
6258					}
6259
6260					Support for data returning statements such as SELECT is driver-specific
6261					and subject to change. At present, the default implementation
6262					provided by DBI only supports non-data returning statements.
6263
6264					Transaction semantics when using array binding are driver and
6265					database specific. If C<AutoCommit> is on, the default DBI
6266					implementation will cause each parameter tuple to be individually
6267					committed (or rolled back in the event of an error). If C<AutoCommit>
6268					is off, the application is responsible for explicitly committing
6269					the entire set of bound parameter tuples. Note that different
6270					drivers and databases may have different behaviours when some
6271					parameter tuples cause failures. In some cases, the driver or
6272					database may automatically rollback the effect of all prior parameter
6273					tuples that succeeded in the transaction; other drivers or databases
6274					may retain the effect of prior successfully executed parameter
6275					tuples. Be sure to check your driver and database for its specific
6276					behaviour.
6277
6278					Note that, in general, performance will usually be better with
6279					C<AutoCommit> turned off, and using explicit C<commit> after each
6280					C<execute_array> call.
6281
6282					The C<execute_array> method was added in DBI 1.22, and ArrayTupleFetch
6283					was added in 1.36.
6284
6285					=head3 C<execute_for_fetch>
6286
6287					$tuples = $sth->execute_for_fetch($fetch_tuple_sub);
6288					$tuples = $sth->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
6289
6290					($tuples, $rows) = $sth->execute_for_fetch($fetch_tuple_sub);
6291					($tuples, $rows) = $sth->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
6292
6293					The execute_for_fetch() method is used to perform bulk operations and
6294					although it is most often used via the execute_array() method you can
6295					use it directly. The main difference between execute_array and
6296					execute_for_fetch is the former does column or row-wise binding and
6297					the latter uses row-wise binding.
6298
6299					The fetch subroutine, referenced by $fetch_tuple_sub, is expected
6300					to return a reference to an array (known as a 'tuple') or undef.
6301
6302					The execute_for_fetch() method calls $fetch_tuple_sub, without any
6303					parameters, until it returns a false value. Each tuple returned is
6304					used to provide bind values for an $sth->execute(@$tuple) call.
6305
6306					In scalar context execute_for_fetch() returns C<undef> if there were any
6307					errors and the number of tuples executed otherwise. Like execute() and
6308					execute_array() a zero is returned as "0E0" so execute_for_fetch() is
6309					only false on error. If there were any errors the @tuple_status array
6310					can be used to discover which tuples failed and with what errors.
6311
6312					When called in list context execute_for_fetch() returns two scalars;
6313					$tuples is the same as calling execute_for_fetch() in scalar context and $rows is
6314					the sum of the number of rows affected for each tuple, if available or -1
6315					if the driver cannot determine this.
6316					If you are doing an update operation the returned rows affected may not be what
6317					you expect if, for instance, one or more of the tuples affected the same row
6318					multiple times. Some drivers may not yet support list context, in which case
6319					$rows will be undef, or may not be able to provide the number of rows affected
6320					when performing this batch operation, in which case $rows will be -1.
6321
6322					If \@tuple_status is passed then the execute_for_fetch method uses
6323					it to return status information. The tuple_status array holds one
6324					element per tuple. If the corresponding execute() did not fail then
6325					the element holds the return value from execute(), which is typically
6326					a row count. If the execute() did fail then the element holds a
6327					reference to an array containing ($sth->err, $sth->errstr, $sth->state).
6328
6329					If the driver detects an error that it knows means no further tuples can be
6330					executed then it may return, with an error status, even though $fetch_tuple_sub
6331					may still have more tuples to be executed.
6332
6333					Although each tuple returned by $fetch_tuple_sub is effectively used
6334					to call $sth->execute(@$tuple_array_ref) the exact timing may vary.
6335					Drivers are free to accumulate sets of tuples to pass to the
6336					database server in bulk group operations for more efficient execution.
6337					However, the $fetch_tuple_sub is specifically allowed to return
6338					the same array reference each time (which is what fetchrow_arrayref()
6339					usually does).
6340
6341					For example:
6342
6343					my $sel = $dbh1->prepare("select foo, bar from table1");
6344					$sel->execute;
6345
6346					my $ins = $dbh2->prepare("insert into table2 (foo, bar) values (?,?)");
6347					my $fetch_tuple_sub = sub { $sel->fetchrow_arrayref };
6348
6349					my @tuple_status;
6350					$rc = $ins->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
6351					my @errors = grep { ref $_ } @tuple_status;
6352
6353					Similarly, if you already have an array containing the data rows
6354					to be processed you'd use a subroutine to shift off and return
6355					each array ref in turn:
6356
6357					$ins->execute_for_fetch( sub { shift @array_of_arrays }, \@tuple_status);
6358
6359					The C<execute_for_fetch> method was added in DBI 1.38.
6360
6361
6362					=head3 C<fetchrow_arrayref>
6363
6364					$ary_ref = $sth->fetchrow_arrayref;
6365					$ary_ref = $sth->fetch; # alias
6366
6367					Fetches the next row of data and returns a reference to an array
6368					holding the field values. Null fields are returned as C<undef>
6369					values in the array.
6370					This is the fastest way to fetch data, particularly if used with
6371					C<$sth-E<gt>bind_columns>.
6372
6373					If there are no more rows or if an error occurs, then C<fetchrow_arrayref>
6374					returns an C<undef>. You should check C<$sth-E<gt>err> afterwards (or use the
6375					C<RaiseError> attribute) to discover if the C<undef> returned was due to an
6376					error.
6377
6378					Note that the same array reference is returned for each fetch, so don't
6379					store the reference and then use it after a later fetch. Also, the
6380					elements of the array are also reused for each row, so take care if you
6381					want to take a reference to an element. See also L</bind_columns>.
6382
6383					=head3 C<fetchrow_array>
6384
6385					@ary = $sth->fetchrow_array;
6386
6387					An alternative to C<fetchrow_arrayref>. Fetches the next row of data
6388					and returns it as a list containing the field values. Null fields
6389					are returned as C<undef> values in the list.
6390
6391					If there are no more rows or if an error occurs, then C<fetchrow_array>
6392					returns an empty list. You should check C<$sth-E<gt>err> afterwards (or use
6393					the C<RaiseError> attribute) to discover if the empty list returned was
6394					due to an error.
6395
6396					If called in a scalar context for a statement handle that has more
6397					than one column, it is undefined whether the driver will return
6398					the value of the first column or the last. So don't do that.
6399					Also, in a scalar context, an C<undef> is returned if there are no
6400					more rows or if an error occurred. That C<undef> can't be distinguished
6401					from an C<undef> returned because the first field value was NULL.
6402					For these reasons you should exercise some caution if you use
6403					C<fetchrow_array> in a scalar context.
6404
6405					=head3 C<fetchrow_hashref>
6406
6407					$hash_ref = $sth->fetchrow_hashref;
6408					$hash_ref = $sth->fetchrow_hashref($name);
6409
6410					An alternative to C<fetchrow_arrayref>. Fetches the next row of data
6411					and returns it as a reference to a hash containing field name and field
6412					value pairs. Null fields are returned as C<undef> values in the hash.
6413
6414					If there are no more rows or if an error occurs, then C<fetchrow_hashref>
6415					returns an C<undef>. You should check C<$sth-E<gt>err> afterwards (or use the
6416					C<RaiseError> attribute) to discover if the C<undef> returned was due to an
6417					error.
6418
6419					The optional C<$name> parameter specifies the name of the statement handle
6420					attribute. For historical reasons it defaults to "C<NAME>", however using
6421					either "C<NAME_lc>" or "C<NAME_uc>" is recommended for portability.
6422
6423					The keys of the hash are the same names returned by C<$sth-E<gt>{$name}>. If
6424					more than one field has the same name, there will only be one entry in the
6425					returned hash for those fields, so statements like "C<select foo, foo from bar>"
6426					will return only a single key from C<fetchrow_hashref>. In these cases use
6427					column aliases or C<fetchrow_arrayref>. Note that it is the database server
6428					(and not the DBD implementation) which provides the I<name> for fields
6429					containing functions like "C<count(*)>" or "C<max(c_foo)>" and they may clash
6430					with existing column names (most databases don't care about duplicate column
6431					names in a result-set). If you want these to return as unique names that are
6432					the same across databases, use I<aliases>, as in "C<select count(*) as cnt>"
6433					or "C<select max(c_foo) mx_foo, ...>" depending on the syntax your database
6434					supports.
6435
6436					Because of the extra work C<fetchrow_hashref> and Perl have to perform, it
6437					is not as efficient as C<fetchrow_arrayref> or C<fetchrow_array>.
6438
6439					By default a reference to a new hash is returned for each row.
6440					It is likely that a future version of the DBI will support an
6441					attribute which will enable the same hash to be reused for each
6442					row. This will give a significant performance boost, but it won't
6443					be enabled by default because of the risk of breaking old code.
6444
6445
6446					=head3 C<fetchall_arrayref>
6447
6448					$tbl_ary_ref = $sth->fetchall_arrayref;
6449					$tbl_ary_ref = $sth->fetchall_arrayref( $slice );
6450					$tbl_ary_ref = $sth->fetchall_arrayref( $slice, $max_rows );
6451
6452					The C<fetchall_arrayref> method can be used to fetch all the data to be
6453					returned from a prepared and executed statement handle. It returns a
6454					reference to an array that contains one reference per row.
6455
6456					If called on an I<inactive> statement handle, C<fetchall_arrayref> returns undef.
6457
6458					If there are no rows left to return from an I<active> statement handle, C<fetchall_arrayref> returns a reference
6459					to an empty array. If an error occurs, C<fetchall_arrayref> returns the
6460					data fetched thus far, which may be none. You should check C<$sth-E<gt>err>
6461					afterwards (or use the C<RaiseError> attribute) to discover if the data is
6462					complete or was truncated due to an error.
6463
6464					If $slice is an array reference, C<fetchall_arrayref> uses L</fetchrow_arrayref>
6465					to fetch each row as an array ref. If the $slice array is not empty
6466					then it is used as a slice to select individual columns by perl array
6467					index number (starting at 0, unlike column and parameter numbers which
6468					start at 1).
6469
6470					With no parameters, or if $slice is undefined, C<fetchall_arrayref>
6471					acts as if passed an empty array ref.
6472
6473					For example, to fetch just the first column of every row:
6474
6475					$tbl_ary_ref = $sth->fetchall_arrayref([0]);
6476
6477					To fetch the second to last and last column of every row:
6478
6479					$tbl_ary_ref = $sth->fetchall_arrayref([-2,-1]);
6480
6481					Those two examples both return a reference to an array of array refs.
6482
6483					If $slice is a hash reference, C<fetchall_arrayref> fetches each row as a hash
6484					reference. If the $slice hash is empty then the keys in the hashes have
6485					whatever name lettercase is returned by default. (See L</FetchHashKeyName>
6486					attribute.) If the $slice hash is I<not> empty, then it is used as a slice to
6487					select individual columns by name. The values of the hash should be set to 1.
6488					The key names of the returned hashes match the letter case of the names in the
6489					parameter hash, regardless of the L</FetchHashKeyName> attribute.
6490
6491					For example, to fetch all fields of every row as a hash ref:
6492
6493					$tbl_ary_ref = $sth->fetchall_arrayref({});
6494
6495					To fetch only the fields called "foo" and "bar" of every row as a hash ref
6496					(with keys named "foo" and "BAR", regardless of the original capitalization):
6497
6498					$tbl_ary_ref = $sth->fetchall_arrayref({ foo=>1, BAR=>1 });
6499
6500					Those two examples both return a reference to an array of hash refs.
6501
6502					If $slice is a I<reference to a hash reference>, that hash is used to select
6503					and rename columns. The keys are 0-based column index numbers and the values
6504					are the corresponding keys for the returned row hashes.
6505
6506					For example, to fetch only the first and second columns of every row as a hash
6507					ref (with keys named "k" and "v" regardless of their original names):
6508
6509					$tbl_ary_ref = $sth->fetchall_arrayref( \{ 0 => 'k', 1 => 'v' } );
6510
6511					If $max_rows is defined and greater than or equal to zero then it
6512					is used to limit the number of rows fetched before returning.
6513					fetchall_arrayref() can then be called again to fetch more rows.
6514					This is especially useful when you need the better performance of
6515					fetchall_arrayref() but don't have enough memory to fetch and return
6516					all the rows in one go.
6517
6518					Here's an example (assumes RaiseError is enabled):
6519
6520					my $rows = []; # cache for batches of rows
6521					while( my $row = ( shift(@$rows) \|\| # get row from cache, or reload cache:
6522					shift(@{$rows=$sth->fetchall_arrayref(undef,10_000)\|\|[]}) )
6523					) {
6524					...
6525					}
6526
6527					That I<might> be the fastest way to fetch and process lots of rows using the DBI,
6528					but it depends on the relative cost of method calls vs memory allocation.
6529
6530					A standard C<while> loop with column binding is often faster because
6531					the cost of allocating memory for the batch of rows is greater than
6532					the saving by reducing method calls. It's possible that the DBI may
6533					provide a way to reuse the memory of a previous batch in future, which
6534					would then shift the balance back towards fetchall_arrayref().
6535
6536
6537					=head3 C<fetchall_hashref>
6538
6539					$hash_ref = $sth->fetchall_hashref($key_field);
6540
6541					The C<fetchall_hashref> method can be used to fetch all the data to be
6542					returned from a prepared and executed statement handle. It returns a reference
6543					to a hash containing a key for each distinct value of the $key_field column
6544					that was fetched. For each key the corresponding value is a reference to a hash
6545					containing all the selected columns and their values, as returned by
6546					C<fetchrow_hashref()>.
6547
6548					If there are no rows to return, C<fetchall_hashref> returns a reference
6549					to an empty hash. If an error occurs, C<fetchall_hashref> returns the
6550					data fetched thus far, which may be none. You should check
6551					C<$sth-E<gt>err> afterwards (or use the C<RaiseError> attribute) to
6552					discover if the data is complete or was truncated due to an error.
6553
6554					The $key_field parameter provides the name of the field that holds the
6555					value to be used for the key for the returned hash. For example:
6556
6557					$dbh->{FetchHashKeyName} = 'NAME_lc';
6558					$sth = $dbh->prepare("SELECT FOO, BAR, ID, NAME, BAZ FROM TABLE");
6559					$sth->execute;
6560					$hash_ref = $sth->fetchall_hashref('id');
6561					print "Name for id 42 is $hash_ref->{42}->{name}\n";
6562
6563					The $key_field parameter can also be specified as an integer column
6564					number (counting from 1). If $key_field doesn't match any column in
6565					the statement, as a name first then as a number, then an error is
6566					returned.
6567
6568					For queries returning more than one 'key' column, you can specify
6569					multiple column names by passing $key_field as a reference to an
6570					array containing one or more key column names (or index numbers).
6571					For example:
6572
6573					$sth = $dbh->prepare("SELECT foo, bar, baz FROM table");
6574					$sth->execute;
6575					$hash_ref = $sth->fetchall_hashref( [ qw(foo bar) ] );
6576					print "For foo 42 and bar 38, baz is $hash_ref->{42}->{38}->{baz}\n";
6577
6578					The fetchall_hashref() method is normally used only where the key
6579					fields values for each row are unique. If multiple rows are returned
6580					with the same values for the key fields then later rows overwrite
6581					earlier ones.
6582
6583					=head3 C<finish>
6584
6585					$rc = $sth->finish;
6586
6587					Indicate that no more data will be fetched from this statement handle
6588					before it is either executed again or destroyed. You almost certainly
6589					do I<not> need to call this method.
6590
6591					Adding calls to C<finish> after loop that fetches all rows is a common mistake,
6592					don't do it, it can mask genuine problems like uncaught fetch errors.
6593
6594					When all the data has been fetched from a C<SELECT> statement, the driver will
6595					automatically call C<finish> for you. So you should I<not> call it explicitly
6596					I<except> when you know that you've not fetched all the data from a statement
6597					handle I<and> the handle won't be destroyed soon.
6598
6599					The most common example is when you only want to fetch just one row,
6600					but in that case the C<selectrow_*> methods are usually better anyway.
6601
6602					Consider a query like:
6603
6604					SELECT foo FROM table WHERE bar=? ORDER BY baz
6605
6606					on a very large table. When executed, the database server will have to use
6607					temporary buffer space to store the sorted rows. If, after executing
6608					the handle and selecting just a few rows, the handle won't be re-executed for
6609					some time and won't be destroyed, the C<finish> method can be used to tell
6610					the server that the buffer space can be freed.
6611
6612					Calling C<finish> resets the L</Active> attribute for the statement. It
6613					may also make some statement handle attributes (such as C<NAME> and C<TYPE>)
6614					unavailable if they have not already been accessed (and thus cached).
6615
6616					The C<finish> method does not affect the transaction status of the
6617					database connection. It has nothing to do with transactions. It's mostly an
6618					internal "housekeeping" method that is rarely needed.
6619					See also L</disconnect> and the L</Active> attribute.
6620
6621					The C<finish> method should have been called C<discard_pending_rows>.
6622
6623
6624					=head3 C<rows>
6625
6626					$rv = $sth->rows;
6627
6628					Returns the number of rows affected by the last row affecting command,
6629					or -1 if the number of rows is not known or not available.
6630
6631					Generally, you can only rely on a row count after a I<non>-C<SELECT>
6632					C<execute> (for some specific operations like C<UPDATE> and C<DELETE>), or
6633					after fetching all the rows of a C<SELECT> statement.
6634
6635					For C<SELECT> statements, it is generally not possible to know how many
6636					rows will be returned except by fetching them all. Some drivers will
6637					return the number of rows the application has fetched so far, but
6638					others may return -1 until all rows have been fetched. So use of the
6639					C<rows> method or C<$DBI::rows> with C<SELECT> statements is not
6640					recommended.
6641
6642					One alternative method to get a row count for a C<SELECT> is to execute a
6643					"SELECT COUNT(*) FROM ..." SQL statement with the same "..." as your
6644					query and then fetch the row count from that.
6645
6646
6647					=head3 C<bind_col>
6648
6649					$rc = $sth->bind_col($column_number, \$var_to_bind);
6650					$rc = $sth->bind_col($column_number, \$var_to_bind, \%attr );
6651					$rc = $sth->bind_col($column_number, \$var_to_bind, $bind_type );
6652
6653					Binds a Perl variable and/or some attributes to an output column
6654					(field) of a C<SELECT> statement. Column numbers count up from 1.
6655					You do not need to bind output columns in order to fetch data.
6656					For maximum portability between drivers, bind_col() should be called
6657					after execute() and not before.
6658					See also L</bind_columns> for an example.
6659
6660					The binding is performed at a low level using Perl aliasing.
6661					Whenever a row is fetched from the database $var_to_bind appears
6662					to be automatically updated simply because it now refers to the same
6663					memory location as the corresponding column value. This makes using
6664					bound variables very efficient.
6665					Binding a tied variable doesn't work, currently.
6666
6667					The L</bind_param> method
6668					performs a similar, but opposite, function for input variables.
6669
6670					B<Data Types for Column Binding>
6671
6672					The C<\%attr> parameter can be used to hint at the data type
6673					formatting the column should have. For example, you can use:
6674
6675					$sth->bind_col(1, undef, { TYPE => SQL_DATETIME });
6676
6677					to specify that you'd like the column (which presumably is some
6678					kind of datetime type) to be returned in the standard format for
6679					SQL_DATETIME, which is 'YYYY-MM-DD HH:MM:SS', rather than the
6680					native formatting the database would normally use.
6681
6682					There's no $var_to_bind in that example to emphasize the point
6683					that bind_col() works on the underlying column and not just
6684					a particular bound variable.
6685
6686					As a short-cut for the common case, the data type can be passed
6687					directly, in place of the C<\%attr> hash reference. This example is
6688					equivalent to the one above:
6689
6690					$sth->bind_col(1, undef, SQL_DATETIME);
6691
6692					The C<TYPE> value indicates the standard (non-driver-specific) type for
6693					this parameter. To specify the driver-specific type, the driver may
6694					support a driver-specific attribute, such as C<{ ora_type =E<gt> 97 }>.
6695
6696					The SQL_DATETIME and other related constants can be imported using
6697
6698					use DBI qw(:sql_types);
6699
6700					See L</"DBI Constants"> for more information.
6701
6702					Few drivers support specifying a data type via a C<bind_col> call
6703					(most will simply ignore the data type). Fewer still allow the data
6704					type to be altered once set. If you do set a column type the type
6705					should remain sticky through further calls to bind_col for the same
6706					column if the type is not overridden (this is important for instance
6707					when you are using a slice in fetchall_arrayref).
6708
6709					The TYPE attribute for bind_col() was first specified in DBI 1.41.
6710
6711					From DBI 1.611, drivers can use the C<TYPE> attribute to attempt to
6712					cast the bound scalar to a perl type which more closely matches
6713					C<TYPE>. At present DBI supports C<SQL_INTEGER>, C<SQL_DOUBLE> and
6714					C<SQL_NUMERIC>. See L</sql_type_cast> for details of how types are
6715					cast.
6716
6717					B<Other attributes for Column Binding>
6718
6719					The C<\%attr> parameter may also contain the following attributes:
6720
6721					=over
6722
6723					=item C<StrictlyTyped>
6724
6725					If a C<TYPE> attribute is passed to bind_col, then the driver will
6726					attempt to change the bound perl scalar to match the type more
6727					closely. If the bound value cannot be cast to the requested C<TYPE>
6728					then by default it is left untouched and no error is generated. If you
6729					specify C<StrictlyTyped> as 1 and the cast fails, this will generate
6730					an error.
6731
6732					This attribute was first added in DBI 1.611. When 1.611 was released
6733					few drivers actually supported this attribute but DBD::Oracle and
6734					DBD::ODBC should from versions 1.24.
6735
6736					=item C<DiscardString>
6737
6738					When the C<TYPE> attribute is passed to L</bind_col> and the driver
6739					successfully casts the bound perl scalar to a non-string type
6740					then if C<DiscardString> is set to 1, the string portion of the
6741					scalar will be discarded. By default, C<DiscardString> is not set.
6742
6743					This attribute was first added in DBI 1.611. When 1.611 was released
6744					few drivers actually supported this attribute but DBD::Oracle and
6745					DBD::ODBC should from versions 1.24.
6746
6747					=back
6748
6749
6750					=head3 C<bind_columns>
6751
6752					$rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
6753
6754					Calls L</bind_col> for each column of the C<SELECT> statement.
6755
6756					The list of references should have the same number of elements as the number of
6757					columns in the C<SELECT> statement. If it doesn't then C<bind_columns> will
6758					bind the elements given, up to the number of columns, and then return an error.
6759
6760					For maximum portability between drivers, bind_columns() should be called
6761					after execute() and not before.
6762
6763					For example:
6764
6765					$dbh->{RaiseError} = 1; # do this, or check every call for errors
6766					$sth = $dbh->prepare(q{ SELECT region, sales FROM sales_by_region });
6767					$sth->execute;
6768					my ($region, $sales);
6769
6770					# Bind Perl variables to columns:
6771					$rv = $sth->bind_columns(\$region, \$sales);
6772
6773					# you can also use Perl's \(...) syntax (see perlref docs):
6774					# $sth->bind_columns(\($region, $sales));
6775
6776					# Column binding is the most efficient way to fetch data
6777					while ($sth->fetch) {
6778					print "$region: $sales\n";
6779					}
6780
6781					For compatibility with old scripts, the first parameter will be
6782					ignored if it is C<undef> or a hash reference.
6783
6784					Here's a more fancy example that binds columns to the values I<inside>
6785					a hash (thanks to H.Merijn Brand):
6786
6787					$sth->execute;
6788					my %row;
6789					$sth->bind_columns( \( @row{ @{$sth->{NAME_lc} } } ));
6790					while ($sth->fetch) {
6791					print "$row{region}: $row{sales}\n";
6792					}
6793
6794
6795					=head3 C<dump_results>
6796
6797					$rows = $sth->dump_results($maxlen, $lsep, $fsep, $fh);
6798
6799					Fetches all the rows from C<$sth>, calls C<DBI::neat_list> for each row, and
6800					prints the results to C<$fh> (defaults to C<STDOUT>) separated by C<$lsep>
6801					(default C<"\n">). C<$fsep> defaults to C<", "> and C<$maxlen> defaults to 35.
6802
6803					This method is designed as a handy utility for prototyping and
6804					testing queries. Since it uses L</neat_list> to
6805					format and edit the string for reading by humans, it is not recommended
6806					for data transfer applications.
6807
6808
6809					=head2 Statement Handle Attributes
6810
6811					This section describes attributes specific to statement handles. Most
6812					of these attributes are read-only.
6813
6814					Changes to these statement handle attributes do not affect any other
6815					existing or future statement handles.
6816
6817					Attempting to set or get the value of an unknown attribute generates a warning,
6818					except for private driver specific attributes (which all have names
6819					starting with a lowercase letter).
6820
6821					Example:
6822
6823					... = $h->{NUM_OF_FIELDS}; # get/read
6824
6825					Some drivers cannot provide valid values for some or all of these
6826					attributes until after C<$sth-E<gt>execute> has been successfully
6827					called. Typically the attribute will be C<undef> in these situations.
6828
6829					Some attributes, like NAME, are not appropriate to some types of
6830					statement, like SELECT. Typically the attribute will be C<undef>
6831					in these situations.
6832
6833					For drivers which support stored procedures and multiple result sets
6834					(see L</more_results>) these attributes relate to the I<current> result set.
6835
6836					See also L</finish> to learn more about the effect it
6837					may have on some attributes.
6838
6839					=head3 C<NUM_OF_FIELDS>
6840
6841					Type: integer, read-only
6842
6843					Number of fields (columns) in the data the prepared statement may return.
6844					Statements that don't return rows of data, like C<DELETE> and C<CREATE>
6845					set C<NUM_OF_FIELDS> to 0 (though it may be undef in some drivers).
6846
6847
6848					=head3 C<NUM_OF_PARAMS>
6849
6850					Type: integer, read-only
6851
6852					The number of parameters (placeholders) in the prepared statement.
6853					See SUBSTITUTION VARIABLES below for more details.
6854
6855
6856					=head3 C<NAME>
6857
6858					Type: array-ref, read-only
6859
6860					Returns a reference to an array of field names for each column. The
6861					names may contain spaces but should not be truncated or have any
6862					trailing space. Note that the names have the letter case (upper, lower
6863					or mixed) as returned by the driver being used. Portable applications
6864					should use L</NAME_lc> or L</NAME_uc>.
6865
6866					print "First column name: $sth->{NAME}->[0]\n";
6867
6868					Also note that the name returned for (aggregate) functions like C<count(*)>
6869					or C<max(c_foo)> is determined by the database server and not by C<DBI> or
6870					the C<DBD> backend.
6871
6872					=head3 C<NAME_lc>
6873
6874					Type: array-ref, read-only
6875
6876					Like C</NAME> but always returns lowercase names.
6877
6878					=head3 C<NAME_uc>
6879
6880					Type: array-ref, read-only
6881
6882					Like C</NAME> but always returns uppercase names.
6883
6884					=head3 C<NAME_hash>
6885
6886					Type: hash-ref, read-only
6887
6888					=head3 C<NAME_lc_hash>
6889
6890					Type: hash-ref, read-only
6891
6892					=head3 C<NAME_uc_hash>
6893
6894					Type: hash-ref, read-only
6895
6896					The C<NAME_hash>, C<NAME_lc_hash>, and C<NAME_uc_hash> attributes
6897					return column name information as a reference to a hash.
6898
6899					The keys of the hash are the names of the columns. The letter case of
6900					the keys corresponds to the letter case returned by the C<NAME>,
6901					C<NAME_lc>, and C<NAME_uc> attributes respectively (as described above).
6902
6903					The value of each hash entry is the perl index number of the
6904					corresponding column (counting from 0). For example:
6905
6906					$sth = $dbh->prepare("select Id, Name from table");
6907					$sth->execute;
6908					@row = $sth->fetchrow_array;
6909					print "Name $row[ $sth->{NAME_lc_hash}{name} ]\n";
6910
6911
6912					=head3 C<TYPE>
6913
6914					Type: array-ref, read-only
6915
6916					Returns a reference to an array of integer values for each
6917					column. The value indicates the data type of the corresponding column.
6918
6919					The values correspond to the international standards (ANSI X3.135
6920					and ISO/IEC 9075) which, in general terms, means ODBC. Driver-specific
6921					types that don't exactly match standard types should generally return
6922					the same values as an ODBC driver supplied by the makers of the
6923					database. That might include private type numbers in ranges the vendor
6924					has officially registered with the ISO working group:
6925
6926					ftp://sqlstandards.org/SC32/SQL_Registry/
6927
6928					Where there's no vendor-supplied ODBC driver to be compatible with,
6929					the DBI driver can use type numbers in the range that is now
6930					officially reserved for use by the DBI: -9999 to -9000.
6931
6932					All possible values for C<TYPE> should have at least one entry in the
6933					output of the C<type_info_all> method (see L</type_info_all>).
6934
6935					=head3 C<PRECISION>
6936
6937					Type: array-ref, read-only
6938
6939					Returns a reference to an array of integer values for each column.
6940
6941					For numeric columns, the value is the maximum number of digits
6942					(without considering a sign character or decimal point). Note that
6943					the "display size" for floating point types (REAL, FLOAT, DOUBLE)
6944					can be up to 7 characters greater than the precision (for the
6945					sign + decimal point + the letter E + a sign + 2 or 3 digits).
6946
6947					For any character type column the value is the OCTET_LENGTH,
6948					in other words the number of bytes, not characters.
6949
6950					(More recent standards refer to this as COLUMN_SIZE but we stick
6951					with PRECISION for backwards compatibility.)
6952
6953					=head3 C<SCALE>
6954
6955					Type: array-ref, read-only
6956
6957					Returns a reference to an array of integer values for each column.
6958					NULL (C<undef>) values indicate columns where scale is not applicable.
6959
6960					=head3 C<NULLABLE>
6961
6962					Type: array-ref, read-only
6963
6964					Returns a reference to an array indicating the possibility of each
6965					column returning a null. Possible values are C<0>
6966					(or an empty string) = no, C<1> = yes, C<2> = unknown.
6967
6968					print "First column may return NULL\n" if $sth->{NULLABLE}->[0];
6969
6970
6971					=head3 C<CursorName>
6972
6973					Type: string, read-only
6974
6975					Returns the name of the cursor associated with the statement handle, if
6976					available. If not available or if the database driver does not support the
6977					C<"where current of ..."> SQL syntax, then it returns C<undef>.
6978
6979
6980					=head3 C<Database>
6981
6982					Type: dbh, read-only
6983
6984					Returns the parent $dbh of the statement handle.
6985
6986
6987					=head3 C<Statement>
6988
6989					Type: string, read-only
6990
6991					Returns the statement string passed to the L</prepare> method.
6992
6993
6994					=head3 C<ParamValues>
6995
6996					Type: hash ref, read-only
6997
6998					Returns a reference to a hash containing the values currently bound
6999					to placeholders. The keys of the hash are the 'names' of the
7000					placeholders, typically integers starting at 1. Returns undef if
7001					not supported by the driver.
7002
7003					See L</ShowErrorStatement> for an example of how this is used.
7004
7005					* Keys:
7006
7007					If the driver supports C<ParamValues> but no values have been bound
7008					yet then the driver should return a hash with placeholders names
7009					in the keys but all the values undef, but some drivers may return
7010					a ref to an empty hash because they can't pre-determine the names.
7011
7012					It is possible that the keys in the hash returned by C<ParamValues>
7013					are not exactly the same as those implied by the prepared statement.
7014					For example, DBD::Oracle translates 'C<?>' placeholders into 'C<:pN>'
7015					where N is a sequence number starting at 1.
7016
7017					* Values:
7018
7019					It is possible that the values in the hash returned by C<ParamValues>
7020					are not I<exactly> the same as those passed to bind_param() or execute().
7021					The driver may have slightly modified values in some way based on the
7022					TYPE the value was bound with. For example a floating point value
7023					bound as an SQL_INTEGER type may be returned as an integer.
7024					The values returned by C<ParamValues> can be passed to another
7025					bind_param() method with the same TYPE and will be seen by the
7026					database as the same value. See also L</ParamTypes> below.
7027
7028					The C<ParamValues> attribute was added in DBI 1.28.
7029
7030					=head3 C<ParamTypes>
7031
7032					Type: hash ref, read-only
7033
7034					Returns a reference to a hash containing the type information
7035					currently bound to placeholders.
7036					Returns undef if not supported by the driver.
7037
7038					* Keys:
7039
7040					See L</ParamValues> above.
7041
7042					* Values:
7043
7044					The hash values are hashrefs of type information in the same form as that
7045					passed to the various bind_param() methods (See L</bind_param> for the format
7046					and values).
7047
7048					It is possible that the values in the hash returned by C<ParamTypes>
7049					are not exactly the same as those passed to bind_param() or execute().
7050					Param attributes specified using the abbreviated form, like this:
7051
7052					$sth->bind_param(1, SQL_INTEGER);
7053
7054					are returned in the expanded form, as if called like this:
7055
7056					$sth->bind_param(1, { TYPE => SQL_INTEGER });
7057
7058					The driver may have modified the type information in some way based
7059					on the bound values, other hints provided by the prepare()'d
7060					SQL statement, or alternate type mappings required by the driver or target
7061					database system. The driver may also add private keys (with names beginning
7062					with the drivers reserved prefix, e.g., odbc_xxx).
7063
7064					* Example:
7065
7066					The keys and values in the returned hash can be passed to the various
7067					bind_param() methods to effectively reproduce a previous param binding.
7068					For example:
7069
7070					# assuming $sth1 is a previously prepared statement handle
7071					my $sth2 = $dbh->prepare( $sth1->{Statement} );
7072					my $ParamValues = $sth1->{ParamValues} \|\| {};
7073					my $ParamTypes = $sth1->{ParamTypes} \|\| {};
7074					$sth2->bind_param($_, $ParamValues->{$_} $ParamTypes->{$_})
7075					for keys %{ {%$ParamValues, %$ParamTypes} };
7076					$sth2->execute();
7077
7078					The C<ParamTypes> attribute was added in DBI 1.49. Implementation
7079					is the responsibility of individual drivers; the DBI layer default
7080					implementation simply returns undef.
7081
7082
7083					=head3 C<ParamArrays>
7084
7085					Type: hash ref, read-only
7086
7087					Returns a reference to a hash containing the values currently bound to
7088					placeholders with L</execute_array> or L</bind_param_array>. The
7089					keys of the hash are the 'names' of the placeholders, typically
7090					integers starting at 1. Returns undef if not supported by the driver
7091					or no arrays of parameters are bound.
7092
7093					Each key value is an array reference containing a list of the bound
7094					parameters for that column.
7095
7096					For example:
7097
7098					$sth = $dbh->prepare("INSERT INTO staff (id, name) values (?,?)");
7099					$sth->execute_array({},[1,2], ['fred','dave']);
7100					if ($sth->{ParamArrays}) {
7101					foreach $param (keys %{$sth->{ParamArrays}}) {
7102					printf "Parameters for %s : %s\n", $param,
7103					join(",", @{$sth->{ParamArrays}->{$param}});
7104					}
7105					}
7106
7107					It is possible that the values in the hash returned by C<ParamArrays>
7108					are not I<exactly> the same as those passed to L</bind_param_array> or
7109					L</execute_array>. The driver may have slightly modified values in some
7110					way based on the TYPE the value was bound with. For example a floating
7111					point value bound as an SQL_INTEGER type may be returned as an
7112					integer.
7113
7114					It is also possible that the keys in the hash returned by
7115					C<ParamArrays> are not exactly the same as those implied by the
7116					prepared statement. For example, DBD::Oracle translates 'C<?>'
7117					placeholders into 'C<:pN>' where N is a sequence number starting at 1.
7118
7119					=head3 C<RowsInCache>
7120
7121					Type: integer, read-only
7122
7123					If the driver supports a local row cache for C<SELECT> statements, then
7124					this attribute holds the number of un-fetched rows in the cache. If the
7125					driver doesn't, then it returns C<undef>. Note that some drivers pre-fetch
7126					rows on execute, whereas others wait till the first fetch.
7127
7128					See also the L</RowCacheSize> database handle attribute.
7129
7130					=head1 FURTHER INFORMATION
7131
7132					=head2 Catalog Methods
7133
7134					An application can retrieve metadata information from the DBMS by issuing
7135					appropriate queries on the views of the Information Schema. Unfortunately,
7136					C<INFORMATION_SCHEMA> views are seldom supported by the DBMS.
7137					Special methods (catalog methods) are available to return result sets
7138					for a small but important portion of that metadata:
7139
7140					column_info
7141					foreign_key_info
7142					primary_key_info
7143					table_info
7144					statistics_info
7145
7146					All catalog methods accept arguments in order to restrict the result sets.
7147					Passing C<undef> to an optional argument does not constrain the search for
7148					that argument.
7149					However, an empty string ('') is treated as a regular search criteria
7150					and will only match an empty value.
7151
7152					B<Note>: SQL/CLI and ODBC differ in the handling of empty strings. An
7153					empty string will not restrict the result set in SQL/CLI.
7154
7155					Most arguments in the catalog methods accept only I<ordinary values>, e.g.
7156					the arguments of C<primary_key_info()>.
7157					Such arguments are treated as a literal string, i.e. the case is significant
7158					and quote characters are taken literally.
7159
7160					Some arguments in the catalog methods accept I<search patterns> (strings
7161					containing '_' and/or '%'), e.g. the C<$table> argument of C<column_info()>.
7162					Passing '%' is equivalent to leaving the argument C<undef>.
7163
7164					B<Caveat>: The underscore ('_') is valid and often used in SQL identifiers.
7165					Passing such a value to a search pattern argument may return more rows than
7166					expected!
7167					To include pattern characters as literals, they must be preceded by an
7168					escape character which can be achieved with
7169
7170					$esc = $dbh->get_info( 14 ); # SQL_SEARCH_PATTERN_ESCAPE
7171					$search_pattern =~ s/([_%])/$esc$1/g;
7172
7173					The ODBC and SQL/CLI specifications define a way to change the default
7174					behaviour described above: All arguments (except I<list value arguments>)
7175					are treated as I<identifier> if the C<SQL_ATTR_METADATA_ID> attribute is
7176					set to C<SQL_TRUE>.
7177					I<Quoted identifiers> are very similar to I<ordinary values>, i.e. their
7178					body (the string within the quotes) is interpreted literally.
7179					I<Unquoted identifiers> are compared in UPPERCASE.
7180
7181					The DBI (currently) does not support the C<SQL_ATTR_METADATA_ID> attribute,
7182					i.e. it behaves like an ODBC driver where C<SQL_ATTR_METADATA_ID> is set to
7183					C<SQL_FALSE>.
7184
7185
7186					=head2 Transactions
7187
7188					Transactions are a fundamental part of any robust database system. They
7189					protect against errors and database corruption by ensuring that sets of
7190					related changes to the database take place in atomic (indivisible,
7191					all-or-nothing) units.
7192
7193					This section applies to databases that support transactions and where
7194					C<AutoCommit> is off. See L</AutoCommit> for details of using C<AutoCommit>
7195					with various types of databases.
7196
7197					The recommended way to implement robust transactions in Perl
7198					applications is to use C<RaiseError> and S<C<eval { ... }>>
7199					(which is very fast, unlike S<C<eval "...">>). For example:
7200
7201					$dbh->{AutoCommit} = 0; # enable transactions, if possible
7202					$dbh->{RaiseError} = 1;
7203					eval {
7204					foo(...) # do lots of work here
7205					bar(...) # including inserts
7206					baz(...) # and updates
7207					$dbh->commit; # commit the changes if we get this far
7208					};
7209					if ($@) {
7210					warn "Transaction aborted because $@";
7211					# now rollback to undo the incomplete changes
7212					# but do it in an eval{} as it may also fail
7213					eval { $dbh->rollback };
7214					# add other application on-error-clean-up code here
7215					}
7216
7217					If the C<RaiseError> attribute is not set, then DBI calls would need to be
7218					manually checked for errors, typically like this:
7219
7220					$h->method(@args) or die $h->errstr;
7221
7222					With C<RaiseError> set, the DBI will automatically C<die> if any DBI method
7223					call on that handle (or a child handle) fails, so you don't have to
7224					test the return value of each method call. See L</RaiseError> for more
7225					details.
7226
7227					A major advantage of the C<eval> approach is that the transaction will be
7228					properly rolled back if I<any> code (not just DBI calls) in the inner
7229					application dies for any reason. The major advantage of using the
7230					C<$h-E<gt>{RaiseError}> attribute is that all DBI calls will be checked
7231					automatically. Both techniques are strongly recommended.
7232
7233					After calling C<commit> or C<rollback> many drivers will not let you
7234					fetch from a previously active C<SELECT> statement handle that's a child
7235					of the same database handle. A typical way round this is to connect the
7236					the database twice and use one connection for C<SELECT> statements.
7237
7238					See L</AutoCommit> and L</disconnect> for other important information
7239					about transactions.
7240
7241
7242					=head2 Handling BLOB / LONG / Memo Fields
7243
7244					Many databases support "blob" (binary large objects), "long", or similar
7245					datatypes for holding very long strings or large amounts of binary
7246					data in a single field. Some databases support variable length long
7247					values over 2,000,000,000 bytes in length.
7248
7249					Since values of that size can't usually be held in memory, and because
7250					databases can't usually know in advance the length of the longest long
7251					that will be returned from a C<SELECT> statement (unlike other data
7252					types), some special handling is required.
7253
7254					In this situation, the value of the C<$h-E<gt>{LongReadLen}>
7255					attribute is used to determine how much buffer space to allocate
7256					when fetching such fields. The C<$h-E<gt>{LongTruncOk}> attribute
7257					is used to determine how to behave if a fetched value can't fit
7258					into the buffer.
7259
7260					See the description of L</LongReadLen> for more information.
7261
7262					When trying to insert long or binary values, placeholders should be used
7263					since there are often limits on the maximum size of an C<INSERT>
7264					statement and the L</quote> method generally can't cope with binary
7265					data. See L</Placeholders and Bind Values>.
7266
7267
7268					=head2 Simple Examples
7269
7270					Here's a complete example program to select and fetch some data:
7271
7272					my $data_source = "dbi::DriverName:db_name";
7273					my $dbh = DBI->connect($data_source, $user, $password)
7274					or die "Can't connect to $data_source: $DBI::errstr";
7275
7276					my $sth = $dbh->prepare( q{
7277					SELECT name, phone
7278					FROM mytelbook
7279					}) or die "Can't prepare statement: $DBI::errstr";
7280
7281					my $rc = $sth->execute
7282					or die "Can't execute statement: $DBI::errstr";
7283
7284					print "Query will return $sth->{NUM_OF_FIELDS} fields.\n\n";
7285					print "Field names: @{ $sth->{NAME} }\n";
7286
7287					while (($name, $phone) = $sth->fetchrow_array) {
7288					print "$name: $phone\n";
7289					}
7290					# check for problems which may have terminated the fetch early
7291					die $sth->errstr if $sth->err;
7292
7293					$dbh->disconnect;
7294
7295					Here's a complete example program to insert some data from a file.
7296					(This example uses C<RaiseError> to avoid needing to check each call).
7297
7298					my $dbh = DBI->connect("dbi:DriverName:db_name", $user, $password, {
7299					RaiseError => 1, AutoCommit => 0
7300					});
7301
7302					my $sth = $dbh->prepare( q{
7303					INSERT INTO table (name, phone) VALUES (?, ?)
7304					});
7305
7306					open FH, "<phone.csv" or die "Unable to open phone.csv: $!";
7307					while (<FH>) {
7308					chomp;
7309					my ($name, $phone) = split /,/;
7310					$sth->execute($name, $phone);
7311					}
7312					close FH;
7313
7314					$dbh->commit;
7315					$dbh->disconnect;
7316
7317					Here's how to convert fetched NULLs (undefined values) into empty strings:
7318
7319					while($row = $sth->fetchrow_arrayref) {
7320					# this is a fast and simple way to deal with nulls:
7321					foreach (@$row) { $_ = '' unless defined }
7322					print "@$row\n";
7323					}
7324
7325					The C<q{...}> style quoting used in these examples avoids clashing with
7326					quotes that may be used in the SQL statement. Use the double-quote like
7327					C<qq{...}> operator if you want to interpolate variables into the string.
7328					See L<perlop/"Quote and Quote-like Operators"> for more details.
7329
7330					=head2 Threads and Thread Safety
7331
7332					Perl 5.7 and later support a new threading model called iThreads.
7333					(The old "5.005 style" threads are not supported by the DBI.)
7334
7335					In the iThreads model each thread has its own copy of the perl
7336					interpreter. When a new thread is created the original perl
7337					interpreter is 'cloned' to create a new copy for the new thread.
7338
7339					If the DBI and drivers are loaded and handles created before the
7340					thread is created then it will get a cloned copy of the DBI, the
7341					drivers and the handles.
7342
7343					However, the internal pointer data within the handles will refer
7344					to the DBI and drivers in the original interpreter. Using those
7345					handles in the new interpreter thread is not safe, so the DBI detects
7346					this and croaks on any method call using handles that don't belong
7347					to the current thread (except for DESTROY).
7348
7349					Because of this (possibly temporary) restriction, newly created
7350					threads must make their own connections to the database. Handles
7351					can't be shared across threads.
7352
7353					But BEWARE, some underlying database APIs (the code the DBD driver
7354					uses to talk to the database, often supplied by the database vendor)
7355					are not thread safe. If it's not thread safe, then allowing more
7356					than one thread to enter the code at the same time may cause
7357					subtle/serious problems. In some cases allowing more than
7358					one thread to enter the code, even if I<not> at the same time,
7359					can cause problems. You have been warned.
7360
7361					Using DBI with perl threads is not yet recommended for production
7362					environments. For more information see
7363					L<http://www.perlmonks.org/index.pl?node_id=288022>
7364
7365					Note: There is a bug in perl 5.8.2 when configured with threads
7366					and debugging enabled (bug #24463) which causes a DBI test to fail.
7367
7368					=head2 Signal Handling and Canceling Operations
7369
7370					[The following only applies to systems with unix-like signal handling.
7371					I'd welcome additions for other systems, especially Windows.]
7372
7373					The first thing to say is that signal handling in Perl versions less
7374					than 5.8 is I<not> safe. There is always a small risk of Perl
7375					crashing and/or core dumping when, or after, handling a signal
7376					because the signal could arrive and be handled while internal data
7377					structures are being changed. If the signal handling code
7378					used those same internal data structures it could cause all manner
7379					of subtle and not-so-subtle problems. The risk was reduced with
7380					5.4.4 but was still present in all perls up through 5.8.0.
7381
7382					Beginning in perl 5.8.0 perl implements 'safe' signal handling if
7383					your system has the POSIX sigaction() routine. Now when a signal
7384					is delivered perl just makes a note of it but does I<not> run the
7385					%SIG handler. The handling is 'deferred' until a 'safe' moment.
7386
7387					Although this change made signal handling safe, it also lead to
7388					a problem with signals being deferred for longer than you'd like.
7389					If a signal arrived while executing a system call, such as waiting
7390					for data on a network connection, the signal is noted and then the
7391					system call that was executing returns with an EINTR error code
7392					to indicate that it was interrupted. All fine so far.
7393
7394					The problem comes when the code that made the system call sees the
7395					EINTR code and decides it's going to call it again. Perl doesn't
7396					do that, but database code sometimes does. If that happens then the
7397					signal handler doesn't get called until later. Maybe much later.
7398
7399					Fortunately there are ways around this which we'll discuss below.
7400					Unfortunately they make signals unsafe again.
7401
7402					The two most common uses of signals in relation to the DBI are for
7403					canceling operations when the user types Ctrl-C (interrupt), and for
7404					implementing a timeout using C<alarm()> and C<$SIG{ALRM}>.
7405
7406					=over 4
7407
7408					=item Cancel
7409
7410					The DBI provides a C<cancel> method for statement handles. The
7411					C<cancel> method should abort the current operation and is designed
7412					to be called from a signal handler. For example:
7413
7414					$SIG{INT} = sub { $sth->cancel };
7415
7416					However, few drivers implement this (the DBI provides a default
7417					method that just returns C<undef>) and, even if implemented, there
7418					is still a possibility that the statement handle, and even the
7419					parent database handle, will not be usable afterwards.
7420
7421					If C<cancel> returns true, then it has successfully
7422					invoked the database engine's own cancel function. If it returns false,
7423					then C<cancel> failed. If it returns C<undef>, then the database
7424					driver does not have cancel implemented - very few do.
7425
7426					=item Timeout
7427
7428					The traditional way to implement a timeout is to set C<$SIG{ALRM}>
7429					to refer to some code that will be executed when an ALRM signal
7430					arrives and then to call alarm($seconds) to schedule an ALRM signal
7431					to be delivered $seconds in the future. For example:
7432
7433					eval {
7434					local $SIG{ALRM} = sub { die "TIMEOUT\n" }; # N.B. \n required
7435					eval {
7436					alarm($seconds);
7437					... code to execute with timeout here (which may die) ...
7438					};
7439					# outer eval catches alarm that might fire JUST before this alarm(0)
7440					alarm(0); # cancel alarm (if code ran fast)
7441					die "$@" if $@;
7442					};
7443					if ( $@ eq "TIMEOUT\n" ) { ... }
7444					elsif ($@) { ... } # some other error
7445
7446					The first (outer) eval is used to avoid the unlikely but possible
7447					chance that the "code to execute" dies and the alarm fires before it
7448					is cancelled. Without the outer eval, if this happened your program
7449					will die if you have no ALRM handler or a non-local alarm handler
7450					will be called.
7451
7452					Unfortunately, as described above, this won't always work as expected,
7453					depending on your perl version and the underlying database code.
7454
7455					With Oracle for instance (DBD::Oracle), if the system which hosts
7456					the database is down the DBI->connect() call will hang for several
7457					minutes before returning an error.
7458
7459					=back
7460
7461					The solution on these systems is to use the C<POSIX::sigaction()>
7462					routine to gain low level access to how the signal handler is installed.
7463
7464					The code would look something like this (for the DBD-Oracle connect()):
7465
7466					use POSIX qw(:signal_h);
7467
7468					my $mask = POSIX::SigSet->new( SIGALRM ); # signals to mask in the handler
7469					my $action = POSIX::SigAction->new(
7470					sub { die "connect timeout\n" }, # the handler code ref
7471					$mask,
7472					# not using (perl 5.8.2 and later) 'safe' switch or sa_flags
7473					);
7474					my $oldaction = POSIX::SigAction->new();
7475					sigaction( SIGALRM, $action, $oldaction );
7476					my $dbh;
7477					eval {
7478					eval {
7479					alarm(5); # seconds before time out
7480					$dbh = DBI->connect("dbi:Oracle:$dsn" ... );
7481					};
7482					alarm(0); # cancel alarm (if connect worked fast)
7483					die "$@\n" if $@; # connect died
7484					};
7485					sigaction( SIGALRM, $oldaction ); # restore original signal handler
7486					if ( $@ ) {
7487					if ($@ eq "connect timeout\n") {...}
7488					else { # connect died }
7489					}
7490
7491					See previous example for the reasoning around the double eval.
7492
7493					Similar techniques can be used for canceling statement execution.
7494
7495					Unfortunately, this solution is somewhat messy, and it does I<not> work with
7496					perl versions less than perl 5.8 where C<POSIX::sigaction()> appears to be broken.
7497
7498					For a cleaner implementation that works across perl versions, see Lincoln Baxter's
7499					Sys::SigAction module at L<http://search.cpan.org/~lbaxter/Sys-SigAction/>.
7500					The documentation for Sys::SigAction includes an longer discussion
7501					of this problem, and a DBD::Oracle test script.
7502
7503					Be sure to read all the signal handling sections of the L<perlipc> manual.
7504
7505					And finally, two more points to keep firmly in mind. Firstly,
7506					remember that what we've done here is essentially revert to old
7507					style I<unsafe> handling of these signals. So do as little as
7508					possible in the handler. Ideally just die(). Secondly, the handles
7509					in use at the time the signal is handled may not be safe to use
7510					afterwards.
7511
7512
7513					=head2 Subclassing the DBI
7514
7515					DBI can be subclassed and extended just like any other object
7516					oriented module. Before we talk about how to do that, it's important
7517					to be clear about the various DBI classes and how they work together.
7518
7519					By default C<$dbh = DBI-E<gt>connect(...)> returns a $dbh blessed
7520					into the C<DBI::db> class. And the C<$dbh-E<gt>prepare> method
7521					returns an $sth blessed into the C<DBI::st> class (actually it
7522					simply changes the last four characters of the calling handle class
7523					to be C<::st>).
7524
7525					The leading 'C<DBI>' is known as the 'root class' and the extra
7526					'C<::db>' or 'C<::st>' are the 'handle type suffixes'. If you want
7527					to subclass the DBI you'll need to put your overriding methods into
7528					the appropriate classes. For example, if you want to use a root class
7529					of C<MySubDBI> and override the do(), prepare() and execute() methods,
7530					then your do() and prepare() methods should be in the C<MySubDBI::db>
7531					class and the execute() method should be in the C<MySubDBI::st> class.
7532
7533					To setup the inheritance hierarchy the @ISA variable in C<MySubDBI::db>
7534					should include C<DBI::db> and the @ISA variable in C<MySubDBI::st>
7535					should include C<DBI::st>. The C<MySubDBI> root class itself isn't
7536					currently used for anything visible and so, apart from setting @ISA
7537					to include C<DBI>, it can be left empty.
7538
7539					So, having put your overriding methods into the right classes, and
7540					setup the inheritance hierarchy, how do you get the DBI to use them?
7541					You have two choices, either a static method call using the name
7542					of your subclass:
7543
7544					$dbh = MySubDBI->connect(...);
7545
7546					or specifying a C<RootClass> attribute:
7547
7548					$dbh = DBI->connect(..., { RootClass => 'MySubDBI' });
7549
7550					If both forms are used then the attribute takes precedence.
7551
7552					The only differences between the two are that using an explicit
7553					RootClass attribute will a) make the DBI automatically attempt to load
7554					a module by that name if the class doesn't exist, and b) won't call
7555					your MySubDBI::connect() method, if you have one.
7556
7557					When subclassing is being used then, after a successful new
7558					connect, the DBI->connect method automatically calls:
7559
7560					$dbh->connected($dsn, $user, $pass, \%attr);
7561
7562					The default method does nothing. The call is made just to simplify
7563					any post-connection setup that your subclass may want to perform.
7564					The parameters are the same as passed to DBI->connect.
7565					If your subclass supplies a connected method, it should be part of the
7566					MySubDBI::db package.
7567
7568					One more thing to note: you must let the DBI do the handle creation. If you
7569					want to override the connect() method in your *::dr class then it must still
7570					call SUPER::connect to get a $dbh to work with. Similarly, an overridden
7571					prepare() method in *::db must still call SUPER::prepare to get a $sth.
7572					If you try to create your own handles using bless() then you'll find the DBI
7573					will reject them with an "is not a DBI handle (has no magic)" error.
7574
7575					Here's a brief example of a DBI subclass. A more thorough example
7576					can be found in F<t/subclass.t> in the DBI distribution.
7577
7578					package MySubDBI;
7579
7580					use strict;
7581
7582					use DBI;
7583					use vars qw(@ISA);
7584					@ISA = qw(DBI);
7585
7586					package MySubDBI::db;
7587					use vars qw(@ISA);
7588					@ISA = qw(DBI::db);
7589
7590					sub prepare {
7591					my ($dbh, @args) = @_;
7592					my $sth = $dbh->SUPER::prepare(@args)
7593					or return;
7594					$sth->{private_mysubdbi_info} = { foo => 'bar' };
7595					return $sth;
7596					}
7597
7598					package MySubDBI::st;
7599					use vars qw(@ISA);
7600					@ISA = qw(DBI::st);
7601
7602					sub fetch {
7603					my ($sth, @args) = @_;
7604					my $row = $sth->SUPER::fetch(@args)
7605					or return;
7606					do_something_magical_with_row_data($row)
7607					or return $sth->set_err(1234, "The magic failed", undef, "fetch");
7608					return $row;
7609					}
7610
7611					When calling a SUPER::method that returns a handle, be careful to
7612					check the return value before trying to do other things with it in
7613					your overridden method. This is especially important if you want to
7614					set a hash attribute on the handle, as Perl's autovivification will
7615					bite you by (in)conveniently creating an unblessed hashref, which your
7616					method will then return with usually baffling results later on like
7617					the error "dbih_getcom handle HASH(0xa4451a8) is not a DBI handle (has
7618					no magic". It's best to check right after the call and return undef
7619					immediately on error, just like DBI would and just like the example
7620					above.
7621
7622					If your method needs to record an error it should call the set_err()
7623					method with the error code and error string, as shown in the example
7624					above. The error code and error string will be recorded in the
7625					handle and available via C<$h-E<gt>err> and C<$DBI::errstr> etc.
7626					The set_err() method always returns an undef or empty list as
7627					appropriate. Since your method should nearly always return an undef
7628					or empty list as soon as an error is detected it's handy to simply
7629					return what set_err() returns, as shown in the example above.
7630
7631					If the handle has C<RaiseError>, C<PrintError>, or C<HandleError>
7632					etc. set then the set_err() method will honour them. This means
7633					that if C<RaiseError> is set then set_err() won't return in the
7634					normal way but will 'throw an exception' that can be caught with
7635					an C<eval> block.
7636
7637					You can stash private data into DBI handles
7638					via C<$h-E<gt>{private_..._*}>. See the entry under L</ATTRIBUTES
7639					COMMON TO ALL HANDLES> for info and important caveats.
7640
7641
7642					=head1 TRACING
7643
7644					The DBI has a powerful tracing mechanism built in. It enables you
7645					to see what's going on 'behind the scenes', both within the DBI and
7646					the drivers you're using.
7647
7648					=head2 Trace Settings
7649
7650					Which details are written to the trace output is controlled by a
7651					combination of a I<trace level>, an integer from 0 to 15, and a set
7652					of I<trace flags> that are either on or off. Together these are known
7653					as the I<trace settings> and are stored together in a single integer.
7654					For normal use you only need to set the trace level, and generally
7655					only to a value between 1 and 4.
7656
7657					Each handle has its own trace settings, and so does the DBI.
7658					When you call a method the DBI merges the handles settings into its
7659					own for the duration of the call: the trace flags of the handle are
7660					OR'd into the trace flags of the DBI, and if the handle has a higher
7661					trace level then the DBI trace level is raised to match it.
7662					The previous DBI trace settings are restored when the called method
7663					returns.
7664
7665					=head2 Trace Levels
7666
7667					Trace I<levels> are as follows:
7668
7669					0 - Trace disabled.
7670					1 - Trace top-level DBI method calls returning with results or errors.
7671					2 - As above, adding tracing of top-level method entry with parameters.
7672					3 - As above, adding some high-level information from the driver
7673					and some internal information from the DBI.
7674					4 - As above, adding more detailed information from the driver.
7675					This is the first level to trace all the rows being fetched.
7676					5 to 15 - As above but with more and more internal information.
7677
7678					Trace level 1 is best for a simple overview of what's happening.
7679					Trace levels 2 thru 4 a good choice for general purpose tracing.
7680					Levels 5 and above are best reserved for investigating a specific
7681					problem, when you need to see "inside" the driver and DBI.
7682
7683					The trace output is detailed and typically very useful. Much of the
7684					trace output is formatted using the L</neat> function, so strings
7685					in the trace output may be edited and truncated by that function.
7686
7687					=head2 Trace Flags
7688
7689					Trace I<flags> are used to enable tracing of specific activities
7690					within the DBI and drivers. The DBI defines some trace flags and
7691					drivers can define others. DBI trace flag names begin with a capital
7692					letter and driver specific names begin with a lowercase letter, as
7693					usual.
7694
7695					Currently the DBI defines these trace flags:
7696
7697					ALL - turn on all DBI and driver flags (not recommended)
7698					SQL - trace SQL statements executed
7699					(not yet implemented in DBI but implemented in some DBDs)
7700					CON - trace connection process
7701					ENC - trace encoding (unicode translations etc)
7702					(not yet implemented in DBI but implemented in some DBDs)
7703					DBD - trace only DBD messages
7704					(not implemented by all DBDs yet)
7705					TXN - trace transactions
7706					(not implemented in all DBDs yet)
7707
7708					The L</parse_trace_flags> and L</parse_trace_flag> methods are used
7709					to convert trace flag names into the corresponding integer bit flags.
7710
7711					=head2 Enabling Trace
7712
7713					The C<$h-E<gt>trace> method sets the trace settings for a handle
7714					and C<DBI-E<gt>trace> does the same for the DBI.
7715
7716					In addition to the L</trace> method, you can enable the same trace
7717					information, and direct the output to a file, by setting the
7718					C<DBI_TRACE> environment variable before starting Perl.
7719					See L</DBI_TRACE> for more information.
7720
7721					Finally, you can set, or get, the trace settings for a handle using
7722					the C<TraceLevel> attribute.
7723
7724					All of those methods use parse_trace_flags() and so allow you set
7725					both the trace level and multiple trace flags by using a string
7726					containing the trace level and/or flag names separated by vertical
7727					bar ("C<\|>") or comma ("C<,>") characters. For example:
7728
7729					local $h->{TraceLevel} = "3\|SQL\|foo";
7730
7731					=head2 Trace Output
7732
7733					Initially trace output is written to C<STDERR>. Both the
7734					C<$h-E<gt>trace> and C<DBI-E<gt>trace> methods take an optional
7735					$trace_file parameter, which may be either the name of a file to be
7736					opened by DBI in append mode, or a reference to an existing writable
7737					(possibly layered) filehandle. If $trace_file is a filename,
7738					and can be opened in append mode, or $trace_file is a writable
7739					filehandle, then I<all> trace output (currently including that from
7740					other handles) is redirected to that file. A warning is generated
7741					if $trace_file can't be opened or is not writable.
7742
7743					Further calls to trace() without $trace_file do not alter where
7744					the trace output is sent. If $trace_file is undefined, then
7745					trace output is sent to C<STDERR> and, if the prior trace was opened with
7746					$trace_file as a filename, the previous trace file is closed; if $trace_file was
7747					a filehandle, the filehandle is B<not> closed.
7748
7749					B<NOTE>: If $trace_file is specified as a filehandle, the filehandle
7750					should not be closed until all DBI operations are completed, or the
7751					application has reset the trace file via another call to
7752					C<trace()> that changes the trace file.
7753
7754					=head2 Tracing to Layered Filehandles
7755
7756					B<NOTE>:
7757
7758					=over 4
7759
7760					=item *
7761					Tied filehandles are not currently supported, as
7762					tie operations are not available to the PerlIO
7763					methods used by the DBI.
7764
7765					=item *
7766					PerlIO layer support requires Perl version 5.8 or higher.
7767
7768					=back
7769
7770					As of version 5.8, Perl provides the ability to layer various
7771					"disciplines" on an open filehandle via the L<PerlIO> module.
7772
7773					A simple example of using PerlIO layers is to use a scalar as the output:
7774
7775					my $scalar = '';
7776					open( my $fh, "+>:scalar", \$scalar );
7777					$dbh->trace( 2, $fh );
7778
7779					Now all trace output is simply appended to $scalar.
7780
7781					A more complex application of tracing to a layered filehandle is the
7782					use of a custom layer (I<Refer to >L<Perlio::via> I<for details
7783					on creating custom PerlIO layers.>). Consider an application with the
7784					following logger module:
7785
7786					package MyFancyLogger;
7787
7788					sub new
7789					{
7790					my $self = {};
7791					my $fh;
7792					open $fh, '>', 'fancylog.log';
7793					$self->{_fh} = $fh;
7794					$self->{_buf} = '';
7795					return bless $self, shift;
7796					}
7797
7798					sub log
7799					{
7800					my $self = shift;
7801					return unless exists $self->{_fh};
7802					my $fh = $self->{_fh};
7803					$self->{_buf} .= shift;
7804					#
7805					# DBI feeds us pieces at a time, so accumulate a complete line
7806					# before outputing
7807					#
7808					print $fh "At ", scalar localtime(), ':', $self->{_buf}, "\n" and
7809					$self->{_buf} = ''
7810					if $self->{_buf}=~tr/\n//;
7811					}
7812
7813					sub close {
7814					my $self = shift;
7815					return unless exists $self->{_fh};
7816					my $fh = $self->{_fh};
7817					print $fh "At ", scalar localtime(), ':', $self->{_buf}, "\n" and
7818					$self->{_buf} = ''
7819					if $self->{_buf};
7820					close $fh;
7821					delete $self->{_fh};
7822					}
7823
7824					1;
7825
7826					To redirect DBI traces to this logger requires creating
7827					a package for the layer:
7828
7829					package PerlIO::via::MyFancyLogLayer;
7830
7831					sub PUSHED
7832					{
7833					my ($class,$mode,$fh) = @_;
7834					my $logger;
7835					return bless \$logger,$class;
7836					}
7837
7838					sub OPEN {
7839					my ($self, $path, $mode, $fh) = @_;
7840					#
7841					# $path is actually our logger object
7842					#
7843					$$self = $path;
7844					return 1;
7845					}
7846
7847					sub WRITE
7848					{
7849					my ($self, $buf, $fh) = @_;
7850					$$self->log($buf);
7851					return length($buf);
7852					}
7853
7854					sub CLOSE {
7855					my $self = shift;
7856					$$self->close();
7857					return 0;
7858					}
7859
7860					1;
7861
7862
7863					The application can then cause DBI traces to be routed to the
7864					logger using
7865
7866					use PerlIO::via::MyFancyLogLayer;
7867
7868					open my $fh, '>:via(MyFancyLogLayer)', MyFancyLogger->new();
7869
7870					$dbh->trace('SQL', $fh);
7871
7872					Now all trace output will be processed by MyFancyLogger's
7873					log() method.
7874
7875					=head2 Trace Content
7876
7877					Many of the values embedded in trace output are formatted using the neat()
7878					utility function. This means they may be quoted, sanitized, and possibly
7879					truncated if longer than C<$DBI::neat_maxlen>. See L</neat> for more details.
7880
7881					=head2 Tracing Tips
7882
7883					You can add tracing to your own application code using the L</trace_msg> method.
7884
7885					It can sometimes be handy to compare trace files from two different runs of the
7886					same script. However using a tool like C<diff> on the original log output
7887					doesn't work well because the trace file is full of object addresses that may
7888					differ on each run.
7889
7890					The DBI includes a handy utility called dbilogstrip that can be used to
7891					'normalize' the log content. It can be used as a filter like this:
7892
7893					DBI_TRACE=2 perl yourscript.pl ...args1... 2>&1 \| dbilogstrip > dbitrace1.log
7894					DBI_TRACE=2 perl yourscript.pl ...args2... 2>&1 \| dbilogstrip > dbitrace2.log
7895					diff -u dbitrace1.log dbitrace2.log
7896
7897					See L<dbilogstrip> for more information.
7898
7899					=head1 DBI ENVIRONMENT VARIABLES
7900
7901					The DBI module recognizes a number of environment variables, but most of
7902					them should not be used most of the time.
7903					It is better to be explicit about what you are doing to avoid the need
7904					for environment variables, especially in a web serving system where web
7905					servers are stingy about which environment variables are available.
7906
7907					=head2 DBI_DSN
7908
7909					The DBI_DSN environment variable is used by DBI->connect if you do not
7910					specify a data source when you issue the connect.
7911					It should have a format such as "dbi:Driver:databasename".
7912
7913					=head2 DBI_DRIVER
7914
7915					The DBI_DRIVER environment variable is used to fill in the database
7916					driver name in DBI->connect if the data source string starts "dbi::"
7917					(thereby omitting the driver).
7918					If DBI_DSN omits the driver name, DBI_DRIVER can fill the gap.
7919
7920					=head2 DBI_AUTOPROXY
7921
7922					The DBI_AUTOPROXY environment variable takes a string value that starts
7923					"dbi:Proxy:" and is typically followed by "hostname=...;port=...".
7924					It is used to alter the behaviour of DBI->connect.
7925					For full details, see DBI::Proxy documentation.
7926
7927					=head2 DBI_USER
7928
7929					The DBI_USER environment variable takes a string value that is used as
7930					the user name if the DBI->connect call is given undef (as distinct from
7931					an empty string) as the username argument.
7932					Be wary of the security implications of using this.
7933
7934					=head2 DBI_PASS
7935
7936					The DBI_PASS environment variable takes a string value that is used as
7937					the password if the DBI->connect call is given undef (as distinct from
7938					an empty string) as the password argument.
7939					Be extra wary of the security implications of using this.
7940
7941					=head2 DBI_DBNAME (obsolete)
7942
7943					The DBI_DBNAME environment variable takes a string value that is used only when the
7944					obsolescent style of DBI->connect (with driver name as fourth parameter) is used, and
7945					when no value is provided for the first (database name) argument.
7946
7947					=head2 DBI_TRACE
7948
7949					The DBI_TRACE environment variable specifies the global default
7950					trace settings for the DBI at startup. Can also be used to direct
7951					trace output to a file. When the DBI is loaded it does:
7952
7953					DBI->trace(split /=/, $ENV{DBI_TRACE}, 2) if $ENV{DBI_TRACE};
7954
7955					So if C<DBI_TRACE> contains an "C<=>" character then what follows
7956					it is used as the name of the file to append the trace to.
7957
7958					output appended to that file. If the name begins with a number
7959					followed by an equal sign (C<=>), then the number and the equal sign are
7960					stripped off from the name, and the number is used to set the trace
7961					level. For example:
7962
7963					DBI_TRACE=1=dbitrace.log perl your_test_script.pl
7964
7965					On Unix-like systems using a Bourne-like shell, you can do this easily
7966					on the command line:
7967
7968					DBI_TRACE=2 perl your_test_script.pl
7969
7970					See L</TRACING> for more information.
7971
7972					=head2 PERL_DBI_DEBUG (obsolete)
7973
7974					An old variable that should no longer be used; equivalent to DBI_TRACE.
7975
7976					=head2 DBI_PROFILE
7977
7978					The DBI_PROFILE environment variable can be used to enable profiling
7979					of DBI method calls. See L<DBI::Profile> for more information.
7980
7981					=head2 DBI_PUREPERL
7982
7983					The DBI_PUREPERL environment variable can be used to enable the
7984					use of DBI::PurePerl. See L<DBI::PurePerl> for more information.
7985
7986					=head1 WARNING AND ERROR MESSAGES
7987
7988					=head2 Fatal Errors
7989
7990					=over 4
7991
7992					=item Can't call method "prepare" without a package or object reference
7993
7994					The C<$dbh> handle you're using to call C<prepare> is probably undefined because
7995					the preceding C<connect> failed. You should always check the return status of
7996					DBI methods, or use the L</RaiseError> attribute.
7997
7998					=item Can't call method "execute" without a package or object reference
7999
8000					The C<$sth> handle you're using to call C<execute> is probably undefined because
8001					the preceding C<prepare> failed. You should always check the return status of
8002					DBI methods, or use the L</RaiseError> attribute.
8003
8004					=item DBI/DBD internal version mismatch
8005
8006					The DBD driver module was built with a different version of DBI than
8007					the one currently being used. You should rebuild the DBD module under
8008					the current version of DBI.
8009
8010					(Some rare platforms require "static linking". On those platforms, there
8011					may be an old DBI or DBD driver version actually embedded in the Perl
8012					executable being used.)
8013
8014					=item DBD driver has not implemented the AutoCommit attribute
8015
8016					The DBD driver implementation is incomplete. Consult the author.
8017
8018					=item Can't [sg]et %s->{%s}: unrecognised attribute
8019
8020					You attempted to set or get an unknown attribute of a handle. Make
8021					sure you have spelled the attribute name correctly; case is significant
8022					(e.g., "Autocommit" is not the same as "AutoCommit").
8023
8024					=back
8025
8026					=head1 Pure-Perl DBI
8027
8028					A pure-perl emulation of the DBI is included in the distribution
8029					for people using pure-perl drivers who, for whatever reason, can't
8030					install the compiled DBI. See L<DBI::PurePerl>.
8031
8032					=head1 SEE ALSO
8033
8034					=head2 Driver and Database Documentation
8035
8036					Refer to the documentation for the DBD driver that you are using.
8037
8038					Refer to the SQL Language Reference Manual for the database engine that you are using.
8039
8040					=head2 ODBC and SQL/CLI Standards Reference Information
8041
8042					More detailed information about the semantics of certain DBI methods
8043					that are based on ODBC and SQL/CLI standards is available on-line
8044					via microsoft.com, for ODBC, and www.jtc1sc32.org for the SQL/CLI
8045					standard:
8046
8047					DBI method ODBC function SQL/CLI Working Draft
8048					---------- ------------- ---------------------
8049					column_info SQLColumns Page 124
8050					foreign_key_info SQLForeignKeys Page 163
8051					get_info SQLGetInfo Page 214
8052					primary_key_info SQLPrimaryKeys Page 254
8053					table_info SQLTables Page 294
8054					type_info SQLGetTypeInfo Page 239
8055					statistics_info SQLStatistics
8056
8057					To find documentation on the ODBC function you can use
8058					the MSDN search facility at:
8059
8060					http://msdn.microsoft.com/Search
8061
8062					and search for something like C<"SQLColumns returns">.
8063
8064					And for SQL/CLI standard information on SQLColumns you'd read page 124 of
8065					the (very large) SQL/CLI Working Draft available from:
8066
8067					http://jtc1sc32.org/doc/N0701-0750/32N0744T.pdf
8068
8069					=head2 Standards Reference Information
8070
8071					A hyperlinked, browsable version of the BNF syntax for SQL92 (plus
8072					Oracle 7 SQL and PL/SQL) is available here:
8073
8074					http://cui.unige.ch/db-research/Enseignement/analyseinfo/SQL92/BNFindex.html
8075
8076					A BNF syntax for SQL3 is available here:
8077
8078					http://www.sqlstandards.org/SC32/WG3/Progression_Documents/Informal_working_drafts/iso-9075-2-1999.bnf
8079
8080					The following links provide further useful information about SQL.
8081					Some of these are rather dated now but may still be useful.
8082
8083					http://www.jcc.com/SQLPages/jccs_sql.htm
8084					http://www.contrib.andrew.cmu.edu/~shadow/sql.html
8085					http://www.altavista.com/query?q=sql+tutorial
8086
8087
8088					=head2 Books and Articles
8089
8090					Programming the Perl DBI, by Alligator Descartes and Tim Bunce.
8091					L<http://books.perl.org/book/154>
8092
8093					Programming Perl 3rd Ed. by Larry Wall, Tom Christiansen & Jon Orwant.
8094					L<http://books.perl.org/book/134>
8095
8096					Learning Perl by Randal Schwartz.
8097					L<http://books.perl.org/book/101>
8098
8099					Details of many other books related to perl can be found at L<http://books.perl.org>
8100
8101					=head2 Perl Modules
8102
8103					Index of DBI related modules available from CPAN:
8104
8105					https://metacpan.org/search?q=DBD%3A%3A
8106					https://metacpan.org/search?q=DBIx%3A%3A
8107					https://metacpan.org/search?q=DBI
8108
8109					For a good comparison of RDBMS-OO mappers and some OO-RDBMS mappers
8110					(including Class::DBI, Alzabo, and DBIx::RecordSet in the former
8111					category and Tangram and SPOPS in the latter) see the Perl
8112					Object-Oriented Persistence project pages at:
8113
8114					http://poop.sourceforge.net
8115
8116					A similar page for Java toolkits can be found at:
8117
8118					http://c2.com/cgi-bin/wiki?ObjectRelationalToolComparison
8119
8120					=head2 Mailing List
8121
8122					The I<dbi-users> mailing list is the primary means of communication among
8123					users of the DBI and its related modules. For details send email to:
8124
8125					dbi-users-help@perl.org
8126
8127					There are typically between 700 and 900 messages per month. You have
8128					to subscribe in order to be able to post. However you can opt for a
8129					'post-only' subscription.
8130
8131					Mailing list archives (of variable quality) are held at:
8132
8133					http://groups.google.com/groups?group=perl.dbi.users
8134					http://www.xray.mpe.mpg.de/mailing-lists/dbi/
8135					http://www.mail-archive.com/dbi-users%40perl.org/
8136
8137					=head2 Assorted Related WWW Links
8138
8139					The DBI "Home Page":
8140
8141					http://dbi.perl.org/
8142
8143					Other DBI related links:
8144
8145					http://tegan.deltanet.com/~phlip/DBUIdoc.html
8146					http://dc.pm.org/perl_db.html
8147					http://wdvl.com/Authoring/DB/Intro/toc.html
8148					http://www.hotwired.com/webmonkey/backend/tutorials/tutorial1.html
8149					http://bumppo.net/lists/macperl/1999/06/msg00197.html
8150					http://www.perlmonks.org/?node=DBI%20recipes
8151					http://www.perlmonks.org/?node=Speeding%20up%20the%20DBI
8152
8153					Other database related links:
8154
8155					http://www.jcc.com/sql_stnd.html
8156					http://cuiwww.unige.ch/OSG/info/FreeDB/FreeDB.home.html
8157					http://www.connectionstrings.com/
8158
8159					Security, especially the "SQL Injection" attack:
8160
8161					http://www.ngssoftware.com/research/papers.html
8162					http://www.ngssoftware.com/papers/advanced_sql_injection.pdf
8163					http://www.ngssoftware.com/papers/more_advanced_sql_injection.pdf
8164					http://www.esecurityplanet.com/trends/article.php/2243461
8165					http://www.spidynamics.com/papers/SQLInjectionWhitePaper.pdf
8166					http://www.imperva.com/application_defense_center/white_papers/blind_sql_server_injection.html
8167					http://online.securityfocus.com/infocus/1644
8168
8169					Commercial and Data Warehouse Links
8170
8171					http://www.dwinfocenter.org
8172					http://www.datawarehouse.com
8173					http://www.datamining.org
8174					http://www.olapcouncil.org
8175					http://www.idwa.org
8176					http://www.knowledgecenters.org/dwcenter.asp
8177
8178					Recommended Perl Programming Links
8179
8180					http://language.perl.com/style/
8181
8182
8183					=head2 FAQ
8184
8185					See L<http://faq.dbi-support.com/>
8186
8187					=head1 AUTHORS
8188
8189					DBI by Tim Bunce, L<http://www.tim.bunce.name>
8190
8191					This pod text by Tim Bunce, J. Douglas Dunlop, Jonathan Leffler and others.
8192					Perl by Larry Wall and the C<perl5-porters>.
8193
8194					=head1 COPYRIGHT
8195
8196					The DBI module is Copyright (c) 1994-2012 Tim Bunce. Ireland.
8197					All rights reserved.
8198
8199					You may distribute under the terms of either the GNU General Public
8200					License or the Artistic License, as specified in the Perl 5.10.0 README file.
8201
8202					=head1 SUPPORT / WARRANTY
8203
8204					The DBI is free Open Source software. IT COMES WITHOUT WARRANTY OF ANY KIND.
8205
8206					=head2 Support
8207
8208					My consulting company, Data Plan Services, offers annual and
8209					multi-annual support contracts for the DBI. These provide sustained
8210					support for DBI development, and sustained value for you in return.
8211					Contact me for details.
8212
8213					=head2 Sponsor Enhancements
8214
8215					If your company would benefit from a specific new DBI feature,
8216					please consider sponsoring its development. Work is performed
8217					rapidly, and usually on a fixed-price payment-on-delivery basis.
8218					Contact me for details.
8219
8220					Using such targeted financing allows you to contribute to DBI
8221					development, and rapidly get something specific and valuable in return.
8222
8223					=head1 ACKNOWLEDGEMENTS
8224
8225					I would like to acknowledge the valuable contributions of the many
8226					people I have worked with on the DBI project, especially in the early
8227					years (1992-1994). In no particular order: Kevin Stock, Buzz Moschetti,
8228					Kurt Andersen, Ted Lemon, William Hails, Garth Kennedy, Michael Peppler,
8229					Neil S. Briscoe, Jeff Urlwin, David J. Hughes, Jeff Stander,
8230					Forrest D Whitcher, Larry Wall, Jeff Fried, Roy Johnson, Paul Hudson,
8231					Georg Rehfeld, Steve Sizemore, Ron Pool, Jon Meek, Tom Christiansen,
8232					Steve Baumgarten, Randal Schwartz, and a whole lot more.
8233
8234					Then, of course, there are the poor souls who have struggled through
8235					untold and undocumented obstacles to actually implement DBI drivers.
8236					Among their ranks are Jochen Wiedmann, Alligator Descartes, Jonathan
8237					Leffler, Jeff Urlwin, Michael Peppler, Henrik Tougaard, Edwin Pratomo,
8238					Davide Migliavacca, Jan Pazdziora, Peter Haworth, Edmund Mergl, Steve
8239					Williams, Thomas Lowery, and Phlip Plumlee. Without them, the DBI would
8240					not be the practical reality it is today. I'm also especially grateful
8241					to Alligator Descartes for starting work on the first edition of the
8242					"Programming the Perl DBI" book and letting me jump on board.
8243
8244					The DBI and DBD::Oracle were originally developed while I was Technical
8245					Director (CTO) of the Paul Ingram Group in the UK. So I'd especially like
8246					to thank Paul for his generosity and vision in supporting this work for many years.
8247
8248					A couple of specific DBI features have been sponsored by enlightened companies:
8249
8250					The development of the swap_inner_handle() method was sponsored by BizRate.com (L<http://BizRate.com>)
8251
8252					The development of DBD::Gofer and related modules was sponsored by
8253					Shopzilla.com (L<http://Shopzilla.com>), where I currently work.
8254
8255					=head1 CONTRIBUTING
8256
8257					As you can see above, many people have contributed to the DBI and
8258					drivers in many ways over many years.
8259
8260					If you'd like to help then see L<http://dbi.perl.org/contributing>.
8261
8262					If you'd like the DBI to do something new or different then a good way
8263					to make that happen is to do it yourself and send me a patch to the
8264					source code that shows the changes. (But read "Speak before you patch"
8265					below.)
8266
8267					=head2 Browsing the source code repository
8268
8269					Use https://github.com/perl5-dbi/dbi
8270
8271					=head2 How to create a patch using Git
8272
8273					The DBI source code is maintained using Git. To access the source
8274					you'll need to install a Git client. Then, to get the source code, do:
8275
8276					git clone https://github.com/perl5-dbi/dbi.git DBI-git
8277
8278					The source code will now be available in the new subdirectory C<DBI-git>.
8279
8280					When you want to synchronize later, issue the command
8281
8282					git pull --all
8283
8284					Make your changes, test them, test them again until everything passes.
8285					If there are no tests for the new feature you added or a behaviour change,
8286					the change should include a new test. Then commit the changes. Either use
8287
8288					git gui
8289
8290					or
8291
8292					git commit -a -m 'Message to my changes'
8293
8294					If you get any conflicts reported you'll need to fix them first.
8295
8296					Then generate the patch file to be mailed:
8297
8298					git format-patch -1 --attach
8299
8300					which will create a file 0001-.patch (where relates to the commit message).
8301					Read the patch file, as a sanity check, and then email it to dbi-dev@perl.org.
8302
8303					If you have a L<github\|https://github.com> account, you can also fork the
8304					repository, commit your changes to the forked repository and then do a
8305					pull request.
8306
8307					=head2 How to create a patch without Git
8308
8309					Unpack a fresh copy of the distribution:
8310
8311					wget http://cpan.metacpan.org/authors/id/T/TI/TIMB/DBI-1.627.tar.gz
8312					tar xfz DBI-1.627.tar.gz
8313
8314					Rename the newly created top level directory:
8315
8316					mv DBI-1.627 DBI-1.627.your_foo
8317
8318					Edit the contents of DBI-1.627.your_foo/* till it does what you want.
8319
8320					Test your changes and then remove all temporary files:
8321
8322					make test && make distclean
8323
8324					Go back to the directory you originally unpacked the distribution:
8325
8326					cd ..
8327
8328					Unpack I<another> copy of the original distribution you started with:
8329
8330					tar xfz DBI-1.627.tar.gz
8331
8332					Then create a patch file by performing a recursive C<diff> on the two
8333					top level directories:
8334
8335					diff -purd DBI-1.627 DBI-1.627.your_foo > DBI-1.627.your_foo.patch
8336
8337					=head2 Speak before you patch
8338
8339					For anything non-trivial or possibly controversial it's a good idea
8340					to discuss (on dbi-dev@perl.org) the changes you propose before
8341					actually spending time working on them. Otherwise you run the risk
8342					of them being rejected because they don't fit into some larger plans
8343					you may not be aware of.
8344
8345					You can also reach the developers on IRC (chat). If they are on-line,
8346					the most likely place to talk to them is the #dbi channel on irc.perl.org
8347
8348					=head1 TRANSLATIONS
8349
8350					A German translation of this manual (possibly slightly out of date) is
8351					available, thanks to O'Reilly, at:
8352
8353					http://www.oreilly.de/catalog/perldbiger/
8354
8355					Some other translations:
8356
8357					http://cronopio.net/perl/ - Spanish
8358					http://member.nifty.ne.jp/hippo2000/dbimemo.htm - Japanese
8359
8360					=head1 TRAINING
8361
8362					References to DBI related training resources. No recommendation implied.
8363
8364					http://www.treepax.co.uk/
8365					http://www.keller.com/dbweb/
8366
8367					(If you offer professional DBI related training services,
8368					please send me your details so I can add them here.)
8369
8370					=head1 OTHER RELATED WORK AND PERL MODULES
8371
8372					=over 4
8373
8374					=item Apache::DBI by E.Mergl@bawue.de
8375
8376					To be used with the Apache daemon together with an embedded Perl
8377					interpreter like C<mod_perl>. Establishes a database connection which
8378					remains open for the lifetime of the HTTP daemon. This way the CGI
8379					connect and disconnect for every database access becomes superfluous.
8380
8381					=item SQL Parser
8382
8383					See also the L<SQL::Statement> module, SQL parser and engine.
8384
8385					=back
8386
8387					=cut
8388
8389					# LocalWords: DBI