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For xt/tapper-mcp-scheduler-with-db-longrun.t
  Run on Tue May 22 17:18:39 2012
Reported on Tue May 22 17:22:38 2012

Filename/2home/ss5/perl5/perlbrew/perls/perl-5.12.3/lib/site_perl/5.12.3/DBIx/Class/SQLMaker/LimitDialects.pm
StatementsExecuted 43 statements in 2.51ms
Subroutines
Calls P F Exclusive
Time
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Time
Subroutine
511120µs2.85msDBIx::Class::SQLMaker::LimitDialects::::_LimitOffsetDBIx::Class::SQLMaker::LimitDialects::_LimitOffset
51124µs24µsDBIx::Class::SQLMaker::LimitDialects::::__rows_bindtypeDBIx::Class::SQLMaker::LimitDialects::__rows_bindtype
11113µs22µsDBIx::Class::SQLMaker::LimitDialects::::BEGIN@3DBIx::Class::SQLMaker::LimitDialects::BEGIN@3
11111µs49µsDBIx::Class::SQLMaker::LimitDialects::::BEGIN@6DBIx::Class::SQLMaker::LimitDialects::BEGIN@6
1118µs177µsDBIx::Class::SQLMaker::LimitDialects::::BEGIN@7DBIx::Class::SQLMaker::LimitDialects::BEGIN@7
1117µs9µsDBIx::Class::SQLMaker::LimitDialects::::BEGIN@4DBIx::Class::SQLMaker::LimitDialects::BEGIN@4
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_FetchFirstDBIx::Class::SQLMaker::LimitDialects::_FetchFirst
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_FirstSkipDBIx::Class::SQLMaker::LimitDialects::_FirstSkip
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_GenericSubQDBIx::Class::SQLMaker::LimitDialects::_GenericSubQ
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_LimitXYDBIx::Class::SQLMaker::LimitDialects::_LimitXY
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_RowCountOrGenericSubQDBIx::Class::SQLMaker::LimitDialects::_RowCountOrGenericSubQ
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_RowNumDBIx::Class::SQLMaker::LimitDialects::_RowNum
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_RowNumberOverDBIx::Class::SQLMaker::LimitDialects::_RowNumberOver
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_SkipFirstDBIx::Class::SQLMaker::LimitDialects::_SkipFirst
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_TopDBIx::Class::SQLMaker::LimitDialects::_Top
0000s0sDBIx::Class::SQLMaker::LimitDialects::::__ANON__[:333]DBIx::Class::SQLMaker::LimitDialects::__ANON__[:333]
0000s0sDBIx::Class::SQLMaker::LimitDialects::::__offset_bindtypeDBIx::Class::SQLMaker::LimitDialects::__offset_bindtype
0000s0sDBIx::Class::SQLMaker::LimitDialects::::__order_by_is_uniqueDBIx::Class::SQLMaker::LimitDialects::__order_by_is_unique
0000s0sDBIx::Class::SQLMaker::LimitDialects::::__total_bindtypeDBIx::Class::SQLMaker::LimitDialects::__total_bindtype
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_prep_for_skimming_limitDBIx::Class::SQLMaker::LimitDialects::_prep_for_skimming_limit
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_rno_default_orderDBIx::Class::SQLMaker::LimitDialects::_rno_default_order
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_subqueried_limit_attrsDBIx::Class::SQLMaker::LimitDialects::_subqueried_limit_attrs
0000s0sDBIx::Class::SQLMaker::LimitDialects::::_unqualify_colnameDBIx::Class::SQLMaker::LimitDialects::_unqualify_colname
Call graph for these subroutines as a Graphviz dot language file.
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1package DBIx::Class::SQLMaker::LimitDialects;
2
3322µs230µs
# spent 22µs (13+8) within DBIx::Class::SQLMaker::LimitDialects::BEGIN@3 which was called: # once (13µs+8µs) by base::import at line 3
use warnings;
# spent 22µs making 1 call to DBIx::Class::SQLMaker::LimitDialects::BEGIN@3 # spent 8µs making 1 call to warnings::import
4320µs211µs
# spent 9µs (7+2) within DBIx::Class::SQLMaker::LimitDialects::BEGIN@4 which was called: # once (7µs+2µs) by base::import at line 4
use strict;
# spent 9µs making 1 call to DBIx::Class::SQLMaker::LimitDialects::BEGIN@4 # spent 2µs making 1 call to strict::import
5
6324µs286µs
# spent 49µs (11+38) within DBIx::Class::SQLMaker::LimitDialects::BEGIN@6 which was called: # once (11µs+38µs) by base::import at line 6
use List::Util 'first';
# spent 49µs making 1 call to DBIx::Class::SQLMaker::LimitDialects::BEGIN@6 # spent 38µs making 1 call to Exporter::import
732.29ms2346µs
# spent 177µs (8+169) within DBIx::Class::SQLMaker::LimitDialects::BEGIN@7 which was called: # once (8µs+169µs) by base::import at line 7
use namespace::clean;
# spent 177µs making 1 call to DBIx::Class::SQLMaker::LimitDialects::BEGIN@7 # spent 169µs making 1 call to namespace::clean::import
8
9# constants are used not only here, but also in comparison tests
10
# spent 24µs within DBIx::Class::SQLMaker::LimitDialects::__rows_bindtype which was called 5 times, avg 5µs/call: # 5 times (24µs+0s) by DBIx::Class::SQLMaker::LimitDialects::_LimitOffset at line 54, avg 5µs/call
sub __rows_bindtype () {
11536µs +{ sqlt_datatype => 'integer' }
12}
13sub __offset_bindtype () {
14 +{ sqlt_datatype => 'integer' }
15}
16sub __total_bindtype () {
17 +{ sqlt_datatype => 'integer' }
18}
19
20=head1 NAME
21
22DBIx::Class::SQLMaker::LimitDialects - SQL::Abstract::Limit-like functionality for DBIx::Class::SQLMaker
23
24=head1 DESCRIPTION
25
26This module replicates a lot of the functionality originally found in
27L<SQL::Abstract::Limit>. While simple limits would work as-is, the more
28complex dialects that require e.g. subqueries could not be reliably
29implemented without taking full advantage of the metadata locked within
30L<DBIx::Class::ResultSource> classes. After reimplementation of close to
3180% of the L<SQL::Abstract::Limit> functionality it was deemed more
32practical to simply make an independent DBIx::Class-specific limit-dialect
33provider.
34
35=head1 SQL LIMIT DIALECTS
36
37Note that the actual implementations listed below never use C<*> literally.
38Instead proper re-aliasing of selectors and order criteria is done, so that
39the limit dialect are safe to use on joined resultsets with clashing column
40names.
41
42Currently the provided dialects are:
43
44=head2 LimitOffset
45
46 SELECT ... LIMIT $limit OFFSET $offset
47
48Supported by B<PostgreSQL> and B<SQLite>
49
50=cut
51
# spent 2.85ms (120µs+2.73) within DBIx::Class::SQLMaker::LimitDialects::_LimitOffset which was called 5 times, avg 570µs/call: # 5 times (120µs+2.73ms) by DBIx::Class::SQLMaker::select at line 210 of DBIx/Class/SQLMaker.pm, avg 570µs/call
sub _LimitOffset {
5225107µs my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
5352.71ms $sql .= $self->_parse_rs_attrs( $rs_attrs ) . " LIMIT ?";
# spent 2.71ms making 5 calls to DBIx::Class::SQLMaker::_parse_rs_attrs, avg 542µs/call
54524µs push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
# spent 24µs making 5 calls to DBIx::Class::SQLMaker::LimitDialects::__rows_bindtype, avg 5µs/call
55 if ($offset) {
56 $sql .= " OFFSET ?";
57 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset ];
58 }
59 return $sql;
60}
61
62=head2 LimitXY
63
64 SELECT ... LIMIT $offset $limit
65
66Supported by B<MySQL> and any L<SQL::Statement> based DBD
67
68=cut
69sub _LimitXY {
70 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
71 $sql .= $self->_parse_rs_attrs( $rs_attrs ) . " LIMIT ";
72 if ($offset) {
73 $sql .= '?, ';
74 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset ];
75 }
76 $sql .= '?';
77 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
78
79 return $sql;
80}
81
82=head2 RowNumberOver
83
84 SELECT * FROM (
85 SELECT *, ROW_NUMBER() OVER( ORDER BY ... ) AS RNO__ROW__INDEX FROM (
86 SELECT ...
87 )
88 ) WHERE RNO__ROW__INDEX BETWEEN ($offset+1) AND ($limit+$offset)
89
90
91ANSI standard Limit/Offset implementation. Supported by B<DB2> and
92B<< MSSQL >= 2005 >>.
93
94=cut
95sub _RowNumberOver {
96 my ($self, $sql, $rs_attrs, $rows, $offset ) = @_;
97
98 # get selectors, and scan the order_by (if any)
99 my ($stripped_sql, $in_sel, $out_sel, $alias_map, $extra_order_sel)
100 = $self->_subqueried_limit_attrs ( $sql, $rs_attrs );
101
102 # make up an order if none exists
103 my $requested_order = (delete $rs_attrs->{order_by}) || $self->_rno_default_order;
104 my $rno_ord = $self->_order_by ($requested_order);
105
106 # this is the order supplement magic
107 my $mid_sel = $out_sel;
108 if ($extra_order_sel) {
109 for my $extra_col (sort
110 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
111 keys %$extra_order_sel
112 ) {
113 $in_sel .= sprintf (', %s AS %s',
114 $extra_col,
115 $extra_order_sel->{$extra_col},
116 );
117
118 $mid_sel .= ', ' . $extra_order_sel->{$extra_col};
119 }
120 }
121
122 # and this is order re-alias magic
123 for ($extra_order_sel, $alias_map) {
124 for my $col (keys %$_) {
125 my $re_col = quotemeta ($col);
126 $rno_ord =~ s/$re_col/$_->{$col}/;
127 }
128 }
129
130 # whatever is left of the order_by (only where is processed at this point)
131 my $group_having = $self->_parse_rs_attrs($rs_attrs);
132
133 my $qalias = $self->_quote ($rs_attrs->{alias});
134 my $idx_name = $self->_quote ('rno__row__index');
135
136 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1], [ $self->__total_bindtype => $offset + $rows ];
137
138 return <<EOS;
139
140SELECT $out_sel FROM (
141 SELECT $mid_sel, ROW_NUMBER() OVER( $rno_ord ) AS $idx_name FROM (
142 SELECT $in_sel ${stripped_sql}${group_having}
143 ) $qalias
144) $qalias WHERE $idx_name >= ? AND $idx_name <= ?
145
146EOS
147
148}
149
150# some databases are happy with OVER (), some need OVER (ORDER BY (SELECT (1)) )
151sub _rno_default_order {
152 return undef;
153}
154
155=head2 SkipFirst
156
157 SELECT SKIP $offset FIRST $limit * FROM ...
158
159Suported by B<Informix>, almost like LimitOffset. According to
160L<SQL::Abstract::Limit> C<... SKIP $offset LIMIT $limit ...> is also supported.
161
162=cut
163sub _SkipFirst {
164 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
165
166 $sql =~ s/^ \s* SELECT \s+ //ix
167 or $self->throw_exception("Unrecognizable SELECT: $sql");
168
169 return sprintf ('SELECT %s%s%s%s',
170 $offset
171 ? do {
172 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset];
173 'SKIP ? '
174 }
175 : ''
176 ,
177 do {
178 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
179 'FIRST ? '
180 },
181 $sql,
182 $self->_parse_rs_attrs ($rs_attrs),
183 );
184}
185
186=head2 FirstSkip
187
188 SELECT FIRST $limit SKIP $offset * FROM ...
189
190Supported by B<Firebird/Interbase>, reverse of SkipFirst. According to
191L<SQL::Abstract::Limit> C<... ROWS $limit TO $offset ...> is also supported.
192
193=cut
194sub _FirstSkip {
195 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
196
197 $sql =~ s/^ \s* SELECT \s+ //ix
198 or $self->throw_exception("Unrecognizable SELECT: $sql");
199
200 return sprintf ('SELECT %s%s%s%s',
201 do {
202 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
203 'FIRST ? '
204 },
205 $offset
206 ? do {
207 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset];
208 'SKIP ? '
209 }
210 : ''
211 ,
212 $sql,
213 $self->_parse_rs_attrs ($rs_attrs),
214 );
215}
216
217
218=head2 RowNum
219
220Depending on the resultset attributes one of:
221
222 SELECT * FROM (
223 SELECT *, ROWNUM rownum__index FROM (
224 SELECT ...
225 ) WHERE ROWNUM <= ($limit+$offset)
226 ) WHERE rownum__index >= ($offset+1)
227
228or
229
230 SELECT * FROM (
231 SELECT *, ROWNUM rownum__index FROM (
232 SELECT ...
233 )
234 ) WHERE rownum__index BETWEEN ($offset+1) AND ($limit+$offset)
235
236or
237
238 SELECT * FROM (
239 SELECT ...
240 ) WHERE ROWNUM <= ($limit+1)
241
242Supported by B<Oracle>.
243
244=cut
245sub _RowNum {
246 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
247
248 my ($stripped_sql, $insel, $outsel) = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
249
250 my $qalias = $self->_quote ($rs_attrs->{alias});
251 my $idx_name = $self->_quote ('rownum__index');
252 my $order_group_having = $self->_parse_rs_attrs($rs_attrs);
253
254 #
255 # There are two ways to limit in Oracle, one vastly faster than the other
256 # on large resultsets: https://decipherinfosys.wordpress.com/2007/08/09/paging-and-countstopkey-optimization/
257 # However Oracle is retarded and does not preserve stable ROWNUM() values
258 # when called twice in the same scope. Therefore unless the resultset is
259 # ordered by a unique set of columns, it is not safe to use the faster
260 # method, and the slower BETWEEN query is used instead
261 #
262 # FIXME - this is quite expensive, and doe snot perform caching of any sort
263 # as soon as some of the DQ work becomes viable consider switching this
264 # over
265 if ( __order_by_is_unique($rs_attrs) ) {
266
267 # if offset is 0 (first page) the we can skip a subquery
268 if (! $offset) {
269 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
270
271 return <<EOS;
272SELECT $outsel FROM (
273 SELECT $insel ${stripped_sql}${order_group_having}
274) $qalias WHERE ROWNUM <= ?
275EOS
276 }
277 else {
278 push @{$self->{limit_bind}}, [ $self->__total_bindtype => $offset + $rows ], [ $self->__offset_bindtype => $offset + 1 ];
279
280 return <<EOS;
281SELECT $outsel FROM (
282 SELECT $outsel, ROWNUM $idx_name FROM (
283 SELECT $insel ${stripped_sql}${order_group_having}
284 ) $qalias WHERE ROWNUM <= ?
285) $qalias WHERE $idx_name >= ?
286EOS
287 }
288 }
289 else {
290 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1 ], [ $self->__total_bindtype => $offset + $rows ];
291
292 return <<EOS;
293SELECT $outsel FROM (
294 SELECT $outsel, ROWNUM $idx_name FROM (
295 SELECT $insel ${stripped_sql}${order_group_having}
296 ) $qalias
297) $qalias WHERE $idx_name BETWEEN ? AND ?
298EOS
299 }
300}
301
302# determine if the supplied order_by contains a unique column (set)
303sub __order_by_is_unique {
304 my $rs_attrs = shift;
305 my $rsrc = $rs_attrs->{_rsroot_rsrc};
306 my $order_by = $rs_attrs->{order_by}
307 || return 0;
308
309 my $storage = $rsrc->schema->storage;
310
311 my @order_by_cols = map { $_->[0] } $storage->_extract_order_criteria($order_by)
312 or return 0;
313
314 my $colinfo =
315 $storage->_resolve_column_info($rs_attrs->{from}, \@order_by_cols);
316
317 my $sources = {
318 map {( "$_" => $_ )} map { $_->{-result_source} } values %$colinfo
319 };
320
321 my $supplied_order = {
322 map { $_ => 1 }
323 grep { exists $colinfo->{$_} and ! $colinfo->{$_}{is_nullable} }
324 @order_by_cols
325 };
326
327 return 0 unless keys %$supplied_order;
328
329 for my $uks (
330 map { values %$_ } map { +{ $_->unique_constraints } } values %$sources
331 ) {
332 return 1
333 unless first { ! exists $supplied_order->{$_} } @$uks;
334 }
335
336 return 0;
337}
338
339# used by _Top and _FetchFirst below
340sub _prep_for_skimming_limit {
341 my ( $self, $sql, $rs_attrs ) = @_;
342
343 # get selectors
344 my (%r, $alias_map, $extra_order_sel);
345 ($r{inner_sql}, $r{in_sel}, $r{out_sel}, $alias_map, $extra_order_sel)
346 = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
347
348 my $requested_order = delete $rs_attrs->{order_by};
349 $r{order_by_requested} = $self->_order_by ($requested_order);
350
351 # make up an order unless supplied
352 my $inner_order = ($r{order_by_requested}
353 ? $requested_order
354 : [ map
355 { "$rs_attrs->{alias}.$_" }
356 ( $rs_attrs->{_rsroot_rsrc}->_pri_cols )
357 ]
358 );
359
360 # localise as we already have all the bind values we need
361 {
362 local $self->{order_bind};
363 $r{order_by_inner} = $self->_order_by ($inner_order);
364
365 my @out_chunks;
366 for my $ch ($self->_order_by_chunks ($inner_order)) {
367 $ch = $ch->[0] if ref $ch eq 'ARRAY';
368
369 $ch =~ s/\s+ ( ASC|DESC ) \s* $//ix;
370 my $dir = uc ($1||'ASC');
371
372 push @out_chunks, \join (' ', $ch, $dir eq 'ASC' ? 'DESC' : 'ASC' );
373 }
374
375 $r{order_by_reversed} = $self->_order_by (\@out_chunks);
376 }
377
378 # this is the order supplement magic
379 $r{mid_sel} = $r{out_sel};
380 if ($extra_order_sel) {
381 for my $extra_col (sort
382 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
383 keys %$extra_order_sel
384 ) {
385 $r{in_sel} .= sprintf (', %s AS %s',
386 $extra_col,
387 $extra_order_sel->{$extra_col},
388 );
389
390 $r{mid_sel} .= ', ' . $extra_order_sel->{$extra_col};
391 }
392
393 # since whatever order bindvals there are, they will be realiased
394 # and need to show up in front of the entire initial inner subquery
395 # *unshift* the selector bind stack to make this happen (horrible,
396 # horrible, but we don't have another mechanism yet)
397 unshift @{$self->{select_bind}}, @{$self->{order_bind}};
398 }
399
400 # and this is order re-alias magic
401 for my $map ($extra_order_sel, $alias_map) {
402 for my $col (keys %$map) {
403 my $re_col = quotemeta ($col);
404 $_ =~ s/$re_col/$map->{$col}/
405 for ($r{order_by_reversed}, $r{order_by_requested});
406 }
407 }
408
409 # generate the rest of the sql
410 $r{grpby_having} = $self->_parse_rs_attrs ($rs_attrs);
411
412 $r{quoted_rs_alias} = $self->_quote ($rs_attrs->{alias});
413
414 \%r;
415}
416
417=head2 Top
418
419 SELECT * FROM
420
421 SELECT TOP $limit FROM (
422 SELECT TOP $limit FROM (
423 SELECT TOP ($limit+$offset) ...
424 ) ORDER BY $reversed_original_order
425 ) ORDER BY $original_order
426
427Unreliable Top-based implementation, supported by B<< MSSQL < 2005 >>.
428
429=head3 CAVEAT
430
431Due to its implementation, this limit dialect returns B<incorrect results>
432when $limit+$offset > total amount of rows in the resultset.
433
434=cut
435
436sub _Top {
437 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
438
439 my %l = %{ $self->_prep_for_skimming_limit($sql, $rs_attrs) };
440
441 $sql = sprintf ('SELECT TOP %u %s %s %s %s',
442 $rows + ($offset||0),
443 $l{in_sel},
444 $l{inner_sql},
445 $l{grpby_having},
446 $l{order_by_inner},
447 );
448
449 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
450 $rows,
451 $l{mid_sel},
452 $sql,
453 $l{quoted_rs_alias},
454 $l{order_by_reversed},
455 ) if $offset;
456
457 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
458 $rows,
459 $l{out_sel},
460 $sql,
461 $l{quoted_rs_alias},
462 $l{order_by_requested},
463 ) if ( ($offset && $l{order_by_requested}) || ($l{mid_sel} ne $l{out_sel}) );
464
465 return $sql;
466}
467
468=head2 FetchFirst
469
470 SELECT * FROM
471 (
472 SELECT * FROM (
473 SELECT * FROM (
474 SELECT * FROM ...
475 ) ORDER BY $reversed_original_order
476 FETCH FIRST $limit ROWS ONLY
477 ) ORDER BY $original_order
478 FETCH FIRST $limit ROWS ONLY
479 )
480
481Unreliable FetchFirst-based implementation, supported by B<< IBM DB2 <= V5R3 >>.
482
483=head3 CAVEAT
484
485Due to its implementation, this limit dialect returns B<incorrect results>
486when $limit+$offset > total amount of rows in the resultset.
487
488=cut
489
490sub _FetchFirst {
491 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
492
493 my %l = %{ $self->_prep_for_skimming_limit($sql, $rs_attrs) };
494
495 $sql = sprintf ('SELECT %s %s %s %s FETCH FIRST %u ROWS ONLY',
496 $l{in_sel},
497 $l{inner_sql},
498 $l{grpby_having},
499 $l{order_by_inner},
500 $rows + ($offset||0),
501 );
502
503 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
504 $l{mid_sel},
505 $sql,
506 $l{quoted_rs_alias},
507 $l{order_by_reversed},
508 $rows,
509 ) if $offset;
510
511 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
512 $l{out_sel},
513 $sql,
514 $l{quoted_rs_alias},
515 $l{order_by_requested},
516 $rows,
517 ) if ( ($offset && $l{order_by_requested}) || ($l{mid_sel} ne $l{out_sel}) );
518
519 return $sql;
520}
521
522=head2 RowCountOrGenericSubQ
523
524This is not exactly a limit dialect, but more of a proxy for B<Sybase ASE>.
525If no $offset is supplied the limit is simply performed as:
526
527 SET ROWCOUNT $limit
528 SELECT ...
529 SET ROWCOUNT 0
530
531Otherwise we fall back to L</GenericSubQ>
532
533=cut
534
535sub _RowCountOrGenericSubQ {
536 my $self = shift;
537 my ($sql, $rs_attrs, $rows, $offset) = @_;
538
539 return $self->_GenericSubQ(@_) if $offset;
540
541 return sprintf <<"EOF", $rows, $sql;
542SET ROWCOUNT %d
543%s
544SET ROWCOUNT 0
545EOF
546}
547
548=head2 GenericSubQ
549
550 SELECT * FROM (
551 SELECT ...
552 )
553 WHERE (
554 SELECT COUNT(*) FROM $original_table cnt WHERE cnt.id < $original_table.id
555 ) BETWEEN $offset AND ($offset+$rows-1)
556
557This is the most evil limit "dialect" (more of a hack) for I<really> stupid
558databases. It works by ordering the set by some unique column, and calculating
559the amount of rows that have a less-er value (thus emulating a L</RowNum>-like
560index). Of course this implies the set can only be ordered by a single unique
561column. Also note that this technique can be and often is B<excruciatingly
562slow>.
563
564Currently used by B<Sybase ASE>, due to lack of any other option.
565
566=cut
567sub _GenericSubQ {
568 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
569
570 my $root_rsrc = $rs_attrs->{_rsroot_rsrc};
571 my $root_tbl_name = $root_rsrc->name;
572
573 my ($order_by, @rest) = do {
574 local $self->{quote_char};
575 $self->_order_by_chunks ($rs_attrs->{order_by})
576 };
577
578 unless (
579 $order_by
580 &&
581 ! @rest
582 &&
583 ( ! ref $order_by
584 ||
585 ( ref $order_by eq 'ARRAY' and @$order_by == 1 )
586 )
587 ) {
588 $self->throw_exception (
589 'Generic Subquery Limit does not work on resultsets without an order, or resultsets '
590 . 'with complex order criteria (multicolumn and/or functions). Provide a single, '
591 . 'unique-column order criteria.'
592 );
593 }
594
595 ($order_by) = @$order_by if ref $order_by;
596
597 $order_by =~ s/\s+ ( ASC|DESC ) \s* $//ix;
598 my $direction = lc ($1 || 'asc');
599
600 my ($unq_sort_col) = $order_by =~ /(?:^|\.)([^\.]+)$/;
601
602 my $inf = $root_rsrc->storage->_resolve_column_info (
603 $rs_attrs->{from}, [$order_by, $unq_sort_col]
604 );
605
606 my $ord_colinfo = $inf->{$order_by} || $self->throw_exception("Unable to determine source of order-criteria '$order_by'");
607
608 if ($ord_colinfo->{-result_source}->name ne $root_tbl_name) {
609 $self->throw_exception(sprintf
610 "Generic Subquery Limit order criteria can be only based on the root-source '%s'"
611 . " (aliased as '%s')", $root_rsrc->source_name, $rs_attrs->{alias},
612 );
613 }
614
615 # make sure order column is qualified
616 $order_by = "$rs_attrs->{alias}.$order_by"
617 unless $order_by =~ /^$rs_attrs->{alias}\./;
618
619 my $is_u;
620 my $ucs = { $root_rsrc->unique_constraints };
621 for (values %$ucs ) {
622 if (@$_ == 1 && "$rs_attrs->{alias}.$_->[0]" eq $order_by) {
623 $is_u++;
624 last;
625 }
626 }
627 $self->throw_exception(
628 "Generic Subquery Limit order criteria column '$order_by' must be unique (no unique constraint found)"
629 ) unless $is_u;
630
631 my ($stripped_sql, $in_sel, $out_sel, $alias_map, $extra_order_sel)
632 = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
633
634 my $cmp_op = $direction eq 'desc' ? '>' : '<';
635 my $count_tbl_alias = 'rownum__emulation';
636
637 my $order_sql = $self->_order_by (delete $rs_attrs->{order_by});
638 my $group_having_sql = $self->_parse_rs_attrs($rs_attrs);
639
640 # add the order supplement (if any) as this is what will be used for the outer WHERE
641 $in_sel .= ", $_" for keys %{$extra_order_sel||{}};
642
643 my $rownum_cond;
644 if ($offset) {
645 $rownum_cond = 'BETWEEN ? AND ?';
646
647 push @{$self->{limit_bind}},
648 [ $self->__offset_bindtype => $offset ],
649 [ $self->__total_bindtype => $offset + $rows - 1]
650 ;
651 }
652 else {
653 $rownum_cond = '< ?';
654
655 push @{$self->{limit_bind}},
656 [ $self->__rows_bindtype => $rows ]
657 ;
658 }
659
660 return sprintf ("
661SELECT $out_sel
662 FROM (
663 SELECT $in_sel ${stripped_sql}${group_having_sql}
664 ) %s
665WHERE ( SELECT COUNT(*) FROM %s %s WHERE %s $cmp_op %s ) $rownum_cond
666$order_sql
667 ", map { $self->_quote ($_) } (
668 $rs_attrs->{alias},
669 $root_tbl_name,
670 $count_tbl_alias,
671 "$count_tbl_alias.$unq_sort_col",
672 $order_by,
673 ));
674}
675
676
677# !!! THIS IS ALSO HORRIFIC !!! /me ashamed
678#
679# Generates inner/outer select lists for various limit dialects
680# which result in one or more subqueries (e.g. RNO, Top, RowNum)
681# Any non-root-table columns need to have their table qualifier
682# turned into a column alias (otherwise names in subqueries clash
683# and/or lose their source table)
684#
685# Returns mangled proto-sql, inner/outer strings of SQL QUOTED selectors
686# with aliases (to be used in whatever select statement), and an alias
687# index hashref of QUOTED SEL => QUOTED ALIAS pairs (to maybe be used
688# for string-subst higher up).
689# If an order_by is supplied, the inner select needs to bring out columns
690# used in implicit (non-selected) orders, and the order condition itself
691# needs to be realiased to the proper names in the outer query. Thus we
692# also return a hashref (order doesn't matter) of QUOTED EXTRA-SEL =>
693# QUOTED ALIAS pairs, which is a list of extra selectors that do *not*
694# exist in the original select list
695sub _subqueried_limit_attrs {
696 my ($self, $proto_sql, $rs_attrs) = @_;
697
698 $self->throw_exception(
699 'Limit dialect implementation usable only in the context of DBIC (missing $rs_attrs)'
700 ) unless ref ($rs_attrs) eq 'HASH';
701
702 # mangle the input sql as we will be replacing the selector entirely
703 unless (
704 $rs_attrs->{_selector_sql}
705 and
706 $proto_sql =~ s/^ \s* SELECT \s* \Q$rs_attrs->{_selector_sql}//ix
707 ) {
708 $self->throw_exception("Unrecognizable SELECT: $proto_sql");
709 }
710
711 my ($re_sep, $re_alias) = map { quotemeta $_ } ( $self->{name_sep}, $rs_attrs->{alias} );
712
713 # insulate from the multiple _recurse_fields calls below
714 local $self->{select_bind};
715
716 # correlate select and as, build selection index
717 my (@sel, $in_sel_index);
718 for my $i (0 .. $#{$rs_attrs->{select}}) {
719
720 my $s = $rs_attrs->{select}[$i];
721 my $sql_sel = $self->_recurse_fields ($s);
722 my $sql_alias = (ref $s) eq 'HASH' ? $s->{-as} : undef;
723
724 push @sel, {
725 sql => $sql_sel,
726 unquoted_sql => do {
727 local $self->{quote_char};
728 $self->_recurse_fields ($s);
729 },
730 as =>
731 $sql_alias
732 ||
733 $rs_attrs->{as}[$i]
734 ||
735 $self->throw_exception("Select argument $i ($s) without corresponding 'as'")
736 ,
737 };
738
739 $in_sel_index->{$sql_sel}++;
740 $in_sel_index->{$self->_quote ($sql_alias)}++ if $sql_alias;
741
742 # record unqualified versions too, so we do not have
743 # to reselect the same column twice (in qualified and
744 # unqualified form)
745 if (! ref $s && $sql_sel =~ / $re_sep (.+) $/x) {
746 $in_sel_index->{$1}++;
747 }
748 }
749
750
751 # re-alias and remove any name separators from aliases,
752 # unless we are dealing with the current source alias
753 # (which will transcend the subqueries as it is necessary
754 # for possible further chaining)
755 my (@in_sel, @out_sel, %renamed);
756 for my $node (@sel) {
757 if (
758 $node->{as} =~ / (?<! ^ $re_alias ) \. /x
759 or
760 $node->{unquoted_sql} =~ / (?<! ^ $re_alias ) $re_sep /x
761 ) {
762 $node->{as} = $self->_unqualify_colname($node->{as});
763 my $quoted_as = $self->_quote($node->{as});
764 push @in_sel, sprintf '%s AS %s', $node->{sql}, $quoted_as;
765 push @out_sel, $quoted_as;
766 $renamed{$node->{sql}} = $quoted_as;
767 }
768 else {
769 push @in_sel, $node->{sql};
770 push @out_sel, $self->_quote ($node->{as});
771 }
772 }
773 # see if the order gives us anything
774 my %extra_order_sel;
775 for my $chunk ($self->_order_by_chunks ($rs_attrs->{order_by})) {
776 # order with bind
777 $chunk = $chunk->[0] if (ref $chunk) eq 'ARRAY';
778 $chunk =~ s/\s+ (?: ASC|DESC ) \s* $//ix;
779
780 next if $in_sel_index->{$chunk};
781
782 $extra_order_sel{$chunk} ||= $self->_quote (
783 'ORDER__BY__' . scalar keys %extra_order_sel
784 );
785 }
786
787 return (
788 $proto_sql,
789 (map { join (', ', @$_ ) } (
790 \@in_sel,
791 \@out_sel)
792 ),
793 \%renamed,
794 keys %extra_order_sel ? \%extra_order_sel : (),
795 );
796}
797
798sub _unqualify_colname {
799 my ($self, $fqcn) = @_;
800 $fqcn =~ s/ \. /__/xg;
801 return $fqcn;
802}
803
80414µs1;
805
806=head1 AUTHORS
807
808See L<DBIx::Class/CONTRIBUTORS>.
809
810=head1 LICENSE
811
812You may distribute this code under the same terms as Perl itself.
813
814111µs1159µs=cut