Profile of DBI.pm

Filename	/usr/lib/x86_64-linux-gnu/perl5/5.20/DBI.pm
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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 $dbh;
671	1	14.5ms	unless ($dbh = $drh->$connect_meth($dsn, $user, $pass, $attr)) { # spent 14.5ms 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	9µs	$dbh->{$a} = delete $apply->{$a}; # spent 9µs making 3 calls to DBI::common::STORE, avg 3µs/call
724			}
725			while ( my ($a, $v) = each %$apply) {
726	3	6µs	eval { $dbh->{$a} = $v }; # assign in void context to avoid re-FETCH # spent 6µs 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	10µs	$dbh->{dbi_connect_closure} = $connect_closure if $dbh; # spent 10µs 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			eval qq{package # hide from PAUSE
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			$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			$sth = $dbh->prepare($statement, $attr);
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