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1 | package DBIx::Class::SQLMaker::LimitDialects; |
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2 | |
3 | use warnings; |
4 | use strict; |
5 | |
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6 | use List::Util 'first'; |
7 | use namespace::clean; |
8 | |
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9 | # constants are used not only here, but also in comparison tests |
10 | sub __rows_bindtype () { |
11 | +{ sqlt_datatype => 'integer' } |
12 | } |
13 | sub __offset_bindtype () { |
14 | +{ sqlt_datatype => 'integer' } |
15 | } |
16 | sub __total_bindtype () { |
17 | +{ sqlt_datatype => 'integer' } |
18 | } |
19 | |
d5dedbd6 |
20 | =head1 NAME |
21 | |
22 | DBIx::Class::SQLMaker::LimitDialects - SQL::Abstract::Limit-like functionality for DBIx::Class::SQLMaker |
23 | |
24 | =head1 DESCRIPTION |
25 | |
26 | This module replicates a lot of the functionality originally found in |
27 | L<SQL::Abstract::Limit>. While simple limits would work as-is, the more |
28 | complex dialects that require e.g. subqueries could not be reliably |
29 | implemented without taking full advantage of the metadata locked within |
30 | L<DBIx::Class::ResultSource> classes. After reimplementation of close to |
31 | 80% of the L<SQL::Abstract::Limit> functionality it was deemed more |
32 | practical to simply make an independent DBIx::Class-specific limit-dialect |
33 | provider. |
34 | |
35 | =head1 SQL LIMIT DIALECTS |
36 | |
37 | Note that the actual implementations listed below never use C<*> literally. |
38 | Instead proper re-aliasing of selectors and order criteria is done, so that |
39 | the limit dialect are safe to use on joined resultsets with clashing column |
40 | names. |
41 | |
42 | Currently the provided dialects are: |
43 | |
d5dedbd6 |
44 | =head2 LimitOffset |
45 | |
46 | SELECT ... LIMIT $limit OFFSET $offset |
47 | |
48 | Supported by B<PostgreSQL> and B<SQLite> |
49 | |
50 | =cut |
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51 | sub _LimitOffset { |
fcb7fcbb |
52 | my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_; |
53 | $sql .= $self->_parse_rs_attrs( $rs_attrs ) . " LIMIT ?"; |
54 | push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ]; |
55 | if ($offset) { |
56 | $sql .= " OFFSET ?"; |
57 | push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset ]; |
58 | } |
7fca91be |
59 | return $sql; |
60 | } |
61 | |
d5dedbd6 |
62 | =head2 LimitXY |
63 | |
64 | SELECT ... LIMIT $offset $limit |
65 | |
66 | Supported by B<MySQL> and any L<SQL::Statement> based DBD |
67 | |
68 | =cut |
7fca91be |
69 | sub _LimitXY { |
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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 | |
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79 | return $sql; |
80 | } |
d5dedbd6 |
81 | |
82 | =head2 RowNumberOver |
83 | |
84 | SELECT * FROM ( |
85 | SELECT *, ROW_NUMBER() OVER( ORDER BY ... ) AS RNO__ROW__INDEX FROM ( |
86 | SELECT ... |
87 | ) |
88 | ) WHERE RNO__ROW__INDEX BETWEEN ($offset+1) AND ($limit+$offset) |
89 | |
90 | |
91 | ANSI standard Limit/Offset implementation. Supported by B<DB2> and |
92 | B<< MSSQL >= 2005 >>. |
93 | |
94 | =cut |
7fca91be |
95 | sub _RowNumberOver { |
96 | my ($self, $sql, $rs_attrs, $rows, $offset ) = @_; |
97 | |
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98 | # get selectors, and scan the order_by (if any) |
69d3c270 |
99 | my ($stripped_sql, $in_sel, $out_sel, $alias_map, $extra_order_sel) |
100 | = $self->_subqueried_limit_attrs ( $sql, $rs_attrs ); |
7fca91be |
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 | ); |
7fca91be |
117 | } |
118 | } |
119 | |
120 | # and this is order re-alias magic |
121 | for ($extra_order_sel, $alias_map) { |
122 | for my $col (keys %$_) { |
123 | my $re_col = quotemeta ($col); |
124 | $rno_ord =~ s/$re_col/$_->{$col}/; |
125 | } |
126 | } |
127 | |
128 | # whatever is left of the order_by (only where is processed at this point) |
129 | my $group_having = $self->_parse_rs_attrs($rs_attrs); |
130 | |
131 | my $qalias = $self->_quote ($rs_attrs->{alias}); |
132 | my $idx_name = $self->_quote ('rno__row__index'); |
133 | |
69d3c270 |
134 | push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1], [ $self->__total_bindtype => $offset + $rows ]; |
135 | |
136 | return <<EOS; |
7fca91be |
137 | |
138 | SELECT $out_sel FROM ( |
139 | SELECT $mid_sel, ROW_NUMBER() OVER( $rno_ord ) AS $idx_name FROM ( |
69d3c270 |
140 | SELECT $in_sel ${stripped_sql}${group_having} |
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141 | ) $qalias |
fcb7fcbb |
142 | ) $qalias WHERE $idx_name >= ? AND $idx_name <= ? |
7fca91be |
143 | |
144 | EOS |
145 | |
7fca91be |
146 | } |
147 | |
148 | # some databases are happy with OVER (), some need OVER (ORDER BY (SELECT (1)) ) |
149 | sub _rno_default_order { |
150 | return undef; |
151 | } |
152 | |
d5dedbd6 |
153 | =head2 SkipFirst |
154 | |
155 | SELECT SKIP $offset FIRST $limit * FROM ... |
156 | |
157 | Suported by B<Informix>, almost like LimitOffset. According to |
158 | L<SQL::Abstract::Limit> C<... SKIP $offset LIMIT $limit ...> is also supported. |
159 | |
160 | =cut |
7fca91be |
161 | sub _SkipFirst { |
162 | my ($self, $sql, $rs_attrs, $rows, $offset) = @_; |
163 | |
164 | $sql =~ s/^ \s* SELECT \s+ //ix |
70c28808 |
165 | or $self->throw_exception("Unrecognizable SELECT: $sql"); |
7fca91be |
166 | |
167 | return sprintf ('SELECT %s%s%s%s', |
168 | $offset |
fcb7fcbb |
169 | ? do { |
8b31f62e |
170 | push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset]; |
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171 | 'SKIP ? ' |
172 | } |
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173 | : '' |
174 | , |
fcb7fcbb |
175 | do { |
8b31f62e |
176 | push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ]; |
fcb7fcbb |
177 | 'FIRST ? ' |
178 | }, |
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179 | $sql, |
180 | $self->_parse_rs_attrs ($rs_attrs), |
181 | ); |
182 | } |
183 | |
d5dedbd6 |
184 | =head2 FirstSkip |
185 | |
186 | SELECT FIRST $limit SKIP $offset * FROM ... |
187 | |
188 | Supported by B<Firebird/Interbase>, reverse of SkipFirst. According to |
189 | L<SQL::Abstract::Limit> C<... ROWS $limit TO $offset ...> is also supported. |
190 | |
191 | =cut |
7fca91be |
192 | sub _FirstSkip { |
193 | my ($self, $sql, $rs_attrs, $rows, $offset) = @_; |
194 | |
195 | $sql =~ s/^ \s* SELECT \s+ //ix |
70c28808 |
196 | or $self->throw_exception("Unrecognizable SELECT: $sql"); |
7fca91be |
197 | |
198 | return sprintf ('SELECT %s%s%s%s', |
fcb7fcbb |
199 | do { |
8b31f62e |
200 | push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ]; |
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201 | 'FIRST ? ' |
202 | }, |
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203 | $offset |
fcb7fcbb |
204 | ? do { |
8b31f62e |
205 | push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset]; |
fcb7fcbb |
206 | 'SKIP ? ' |
207 | } |
7fca91be |
208 | : '' |
209 | , |
210 | $sql, |
211 | $self->_parse_rs_attrs ($rs_attrs), |
212 | ); |
213 | } |
214 | |
6a6394f1 |
215 | |
d5dedbd6 |
216 | =head2 RowNum |
217 | |
6a6394f1 |
218 | Depending on the resultset attributes one of: |
219 | |
d5dedbd6 |
220 | SELECT * FROM ( |
221 | SELECT *, ROWNUM rownum__index FROM ( |
222 | SELECT ... |
d9672fb9 |
223 | ) WHERE ROWNUM <= ($limit+$offset) |
224 | ) WHERE rownum__index >= ($offset+1) |
d5dedbd6 |
225 | |
6a6394f1 |
226 | or |
227 | |
228 | SELECT * FROM ( |
229 | SELECT *, ROWNUM rownum__index FROM ( |
230 | SELECT ... |
231 | ) |
232 | ) WHERE rownum__index BETWEEN ($offset+1) AND ($limit+$offset) |
233 | |
234 | or |
235 | |
236 | SELECT * FROM ( |
237 | SELECT ... |
238 | ) WHERE ROWNUM <= ($limit+1) |
239 | |
d5dedbd6 |
240 | Supported by B<Oracle>. |
241 | |
242 | =cut |
7fca91be |
243 | sub _RowNum { |
244 | my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_; |
245 | |
69d3c270 |
246 | my ($stripped_sql, $insel, $outsel) = $self->_subqueried_limit_attrs ($sql, $rs_attrs); |
7fca91be |
247 | |
248 | my $qalias = $self->_quote ($rs_attrs->{alias}); |
249 | my $idx_name = $self->_quote ('rownum__index'); |
250 | my $order_group_having = $self->_parse_rs_attrs($rs_attrs); |
251 | |
6a6394f1 |
252 | # |
253 | # There are two ways to limit in Oracle, one vastly faster than the other |
254 | # on large resultsets: https://decipherinfosys.wordpress.com/2007/08/09/paging-and-countstopkey-optimization/ |
255 | # However Oracle is retarded and does not preserve stable ROWNUM() values |
256 | # when called twice in the same scope. Therefore unless the resultset is |
257 | # ordered by a unique set of columns, it is not safe to use the faster |
258 | # method, and the slower BETWEEN query is used instead |
259 | # |
7cec4356 |
260 | # FIXME - this is quite expensive, and does not perform caching of any sort |
6a6394f1 |
261 | # as soon as some of the DQ work becomes viable consider switching this |
262 | # over |
7cec4356 |
263 | if ( |
264 | $rs_attrs->{order_by} |
265 | and |
266 | $rs_attrs->{_rsroot_rsrc}->storage->_order_by_is_stable( |
267 | $rs_attrs->{from}, $rs_attrs->{order_by} |
268 | ) |
269 | ) { |
6a6394f1 |
270 | # if offset is 0 (first page) the we can skip a subquery |
271 | if (! $offset) { |
272 | push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ]; |
273 | |
274 | return <<EOS; |
275 | SELECT $outsel FROM ( |
276 | SELECT $insel ${stripped_sql}${order_group_having} |
277 | ) $qalias WHERE ROWNUM <= ? |
278 | EOS |
279 | } |
280 | else { |
281 | push @{$self->{limit_bind}}, [ $self->__total_bindtype => $offset + $rows ], [ $self->__offset_bindtype => $offset + 1 ]; |
69d3c270 |
282 | |
6a6394f1 |
283 | return <<EOS; |
7fca91be |
284 | SELECT $outsel FROM ( |
285 | SELECT $outsel, ROWNUM $idx_name FROM ( |
69d3c270 |
286 | SELECT $insel ${stripped_sql}${order_group_having} |
fcb7fcbb |
287 | ) $qalias WHERE ROWNUM <= ? |
288 | ) $qalias WHERE $idx_name >= ? |
7fca91be |
289 | EOS |
6a6394f1 |
290 | } |
d9672fb9 |
291 | } |
292 | else { |
6a6394f1 |
293 | push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1 ], [ $self->__total_bindtype => $offset + $rows ]; |
69d3c270 |
294 | |
295 | return <<EOS; |
6a6394f1 |
296 | SELECT $outsel FROM ( |
297 | SELECT $outsel, ROWNUM $idx_name FROM ( |
69d3c270 |
298 | SELECT $insel ${stripped_sql}${order_group_having} |
6a6394f1 |
299 | ) $qalias |
300 | ) $qalias WHERE $idx_name BETWEEN ? AND ? |
d9672fb9 |
301 | EOS |
6a6394f1 |
302 | } |
303 | } |
7fca91be |
304 | |
6a6394f1 |
305 | # used by _Top and _FetchFirst below |
96eacdb7 |
306 | sub _prep_for_skimming_limit { |
307 | my ( $self, $sql, $rs_attrs ) = @_; |
7fca91be |
308 | |
7fca91be |
309 | # get selectors |
69d3c270 |
310 | my (%r, $alias_map, $extra_order_sel); |
311 | ($r{inner_sql}, $r{in_sel}, $r{out_sel}, $alias_map, $extra_order_sel) |
312 | = $self->_subqueried_limit_attrs ($sql, $rs_attrs); |
7fca91be |
313 | |
314 | my $requested_order = delete $rs_attrs->{order_by}; |
96eacdb7 |
315 | $r{order_by_requested} = $self->_order_by ($requested_order); |
7fca91be |
316 | |
86bb5a27 |
317 | # make up an order unless supplied or sanity check what we are given |
318 | my $inner_order; |
319 | if ($r{order_by_requested}) { |
320 | $self->throw_exception ( |
321 | 'Unable to safely perform "skimming type" limit with supplied unstable order criteria' |
322 | ) unless $rs_attrs->{_rsroot_rsrc}->schema->storage->_order_by_is_stable( |
323 | $rs_attrs->{from}, |
324 | $requested_order |
325 | ); |
326 | |
327 | $inner_order = $requested_order; |
328 | } |
329 | else { |
330 | $inner_order = [ map |
3f5b99fe |
331 | { "$rs_attrs->{alias}.$_" } |
86bb5a27 |
332 | ( @{ |
333 | $rs_attrs->{_rsroot_rsrc}->_identifying_column_set |
334 | || |
335 | $self->throw_exception(sprintf( |
336 | 'Unable to auto-construct stable order criteria for "skimming type" limit ' |
337 | . "dialect based on source '%s'", $rs_attrs->{_rsroot_rsrc}->name) ); |
338 | } ) |
339 | ]; |
340 | } |
7fca91be |
341 | |
7fca91be |
342 | # localise as we already have all the bind values we need |
343 | { |
344 | local $self->{order_bind}; |
96eacdb7 |
345 | $r{order_by_inner} = $self->_order_by ($inner_order); |
7fca91be |
346 | |
347 | my @out_chunks; |
348 | for my $ch ($self->_order_by_chunks ($inner_order)) { |
349 | $ch = $ch->[0] if ref $ch eq 'ARRAY'; |
350 | |
351 | $ch =~ s/\s+ ( ASC|DESC ) \s* $//ix; |
352 | my $dir = uc ($1||'ASC'); |
353 | |
354 | push @out_chunks, \join (' ', $ch, $dir eq 'ASC' ? 'DESC' : 'ASC' ); |
355 | } |
356 | |
96eacdb7 |
357 | $r{order_by_reversed} = $self->_order_by (\@out_chunks); |
7fca91be |
358 | } |
359 | |
360 | # this is the order supplement magic |
96eacdb7 |
361 | $r{mid_sel} = $r{out_sel}; |
7fca91be |
362 | if ($extra_order_sel) { |
363 | for my $extra_col (sort |
364 | { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} } |
365 | keys %$extra_order_sel |
366 | ) { |
96eacdb7 |
367 | $r{in_sel} .= sprintf (', %s AS %s', |
7fca91be |
368 | $extra_col, |
369 | $extra_order_sel->{$extra_col}, |
370 | ); |
371 | |
96eacdb7 |
372 | $r{mid_sel} .= ', ' . $extra_order_sel->{$extra_col}; |
7fca91be |
373 | } |
374 | |
8b31f62e |
375 | # Whatever order bindvals there are, they will be realiased and |
376 | # need to show up in front of the entire initial inner subquery |
377 | push @{$self->{pre_select_bind}}, @{$self->{order_bind}}; |
7fca91be |
378 | } |
379 | |
86bb5a27 |
380 | # if this is a part of something bigger, we need to add back all |
381 | # the extra order_by's, as they may be relied upon by the outside |
382 | # of a prefetch or something |
383 | if ($rs_attrs->{_is_internal_subuery} and keys %$extra_order_sel) { |
384 | $r{out_sel} .= sprintf ", $extra_order_sel->{$_} AS $_" |
385 | for sort |
386 | { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} } |
387 | grep { $_ !~ /[^\w\-]/ } # ignore functions |
388 | keys %$extra_order_sel |
389 | ; |
390 | } |
391 | |
7fca91be |
392 | # and this is order re-alias magic |
393 | for my $map ($extra_order_sel, $alias_map) { |
394 | for my $col (keys %$map) { |
395 | my $re_col = quotemeta ($col); |
396 | $_ =~ s/$re_col/$map->{$col}/ |
96eacdb7 |
397 | for ($r{order_by_reversed}, $r{order_by_requested}); |
7fca91be |
398 | } |
399 | } |
400 | |
401 | # generate the rest of the sql |
96eacdb7 |
402 | $r{grpby_having} = $self->_parse_rs_attrs ($rs_attrs); |
7fca91be |
403 | |
96eacdb7 |
404 | $r{quoted_rs_alias} = $self->_quote ($rs_attrs->{alias}); |
405 | |
406 | \%r; |
407 | } |
408 | |
409 | =head2 Top |
410 | |
411 | SELECT * FROM |
412 | |
413 | SELECT TOP $limit FROM ( |
414 | SELECT TOP $limit FROM ( |
415 | SELECT TOP ($limit+$offset) ... |
416 | ) ORDER BY $reversed_original_order |
417 | ) ORDER BY $original_order |
418 | |
419 | Unreliable Top-based implementation, supported by B<< MSSQL < 2005 >>. |
420 | |
421 | =head3 CAVEAT |
422 | |
423 | Due to its implementation, this limit dialect returns B<incorrect results> |
424 | when $limit+$offset > total amount of rows in the resultset. |
425 | |
426 | =cut |
427 | |
428 | sub _Top { |
429 | my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_; |
430 | |
431 | my %l = %{ $self->_prep_for_skimming_limit($sql, $rs_attrs) }; |
7fca91be |
432 | |
433 | $sql = sprintf ('SELECT TOP %u %s %s %s %s', |
434 | $rows + ($offset||0), |
96eacdb7 |
435 | $l{in_sel}, |
436 | $l{inner_sql}, |
437 | $l{grpby_having}, |
438 | $l{order_by_inner}, |
7fca91be |
439 | ); |
440 | |
441 | $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s', |
442 | $rows, |
96eacdb7 |
443 | $l{mid_sel}, |
7fca91be |
444 | $sql, |
96eacdb7 |
445 | $l{quoted_rs_alias}, |
446 | $l{order_by_reversed}, |
7fca91be |
447 | ) if $offset; |
448 | |
449 | $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s', |
450 | $rows, |
96eacdb7 |
451 | $l{out_sel}, |
452 | $sql, |
453 | $l{quoted_rs_alias}, |
454 | $l{order_by_requested}, |
455 | ) if ( ($offset && $l{order_by_requested}) || ($l{mid_sel} ne $l{out_sel}) ); |
456 | |
457 | return $sql; |
458 | } |
459 | |
460 | =head2 FetchFirst |
461 | |
462 | SELECT * FROM |
463 | ( |
464 | SELECT * FROM ( |
465 | SELECT * FROM ( |
466 | SELECT * FROM ... |
467 | ) ORDER BY $reversed_original_order |
468 | FETCH FIRST $limit ROWS ONLY |
469 | ) ORDER BY $original_order |
470 | FETCH FIRST $limit ROWS ONLY |
471 | ) |
472 | |
473 | Unreliable FetchFirst-based implementation, supported by B<< IBM DB2 <= V5R3 >>. |
474 | |
475 | =head3 CAVEAT |
476 | |
477 | Due to its implementation, this limit dialect returns B<incorrect results> |
478 | when $limit+$offset > total amount of rows in the resultset. |
479 | |
480 | =cut |
481 | |
482 | sub _FetchFirst { |
483 | my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_; |
484 | |
485 | my %l = %{ $self->_prep_for_skimming_limit($sql, $rs_attrs) }; |
486 | |
487 | $sql = sprintf ('SELECT %s %s %s %s FETCH FIRST %u ROWS ONLY', |
488 | $l{in_sel}, |
489 | $l{inner_sql}, |
490 | $l{grpby_having}, |
491 | $l{order_by_inner}, |
492 | $rows + ($offset||0), |
493 | ); |
494 | |
495 | $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY', |
496 | $l{mid_sel}, |
497 | $sql, |
498 | $l{quoted_rs_alias}, |
499 | $l{order_by_reversed}, |
500 | $rows, |
501 | ) if $offset; |
502 | |
503 | $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY', |
504 | $l{out_sel}, |
7fca91be |
505 | $sql, |
96eacdb7 |
506 | $l{quoted_rs_alias}, |
507 | $l{order_by_requested}, |
508 | $rows, |
509 | ) if ( ($offset && $l{order_by_requested}) || ($l{mid_sel} ne $l{out_sel}) ); |
7fca91be |
510 | |
7fca91be |
511 | return $sql; |
512 | } |
513 | |
d5dedbd6 |
514 | =head2 RowCountOrGenericSubQ |
515 | |
516 | This is not exactly a limit dialect, but more of a proxy for B<Sybase ASE>. |
517 | If no $offset is supplied the limit is simply performed as: |
518 | |
519 | SET ROWCOUNT $limit |
520 | SELECT ... |
521 | SET ROWCOUNT 0 |
522 | |
523 | Otherwise we fall back to L</GenericSubQ> |
524 | |
525 | =cut |
96eacdb7 |
526 | |
7fca91be |
527 | sub _RowCountOrGenericSubQ { |
528 | my $self = shift; |
529 | my ($sql, $rs_attrs, $rows, $offset) = @_; |
530 | |
531 | return $self->_GenericSubQ(@_) if $offset; |
532 | |
533 | return sprintf <<"EOF", $rows, $sql; |
534 | SET ROWCOUNT %d |
535 | %s |
536 | SET ROWCOUNT 0 |
537 | EOF |
538 | } |
539 | |
d5dedbd6 |
540 | =head2 GenericSubQ |
541 | |
542 | SELECT * FROM ( |
543 | SELECT ... |
544 | ) |
545 | WHERE ( |
546 | SELECT COUNT(*) FROM $original_table cnt WHERE cnt.id < $original_table.id |
547 | ) BETWEEN $offset AND ($offset+$rows-1) |
548 | |
549 | This is the most evil limit "dialect" (more of a hack) for I<really> stupid |
550 | databases. It works by ordering the set by some unique column, and calculating |
551 | the amount of rows that have a less-er value (thus emulating a L</RowNum>-like |
552 | index). Of course this implies the set can only be ordered by a single unique |
553 | column. Also note that this technique can be and often is B<excruciatingly |
554 | slow>. |
555 | |
556 | Currently used by B<Sybase ASE>, due to lack of any other option. |
557 | |
558 | =cut |
7fca91be |
559 | sub _GenericSubQ { |
560 | my ($self, $sql, $rs_attrs, $rows, $offset) = @_; |
561 | |
4376a157 |
562 | my $root_rsrc = $rs_attrs->{_rsroot_rsrc}; |
7fca91be |
563 | my $root_tbl_name = $root_rsrc->name; |
564 | |
528e717e |
565 | my ($first_order_by) = do { |
7fca91be |
566 | local $self->{quote_char}; |
528e717e |
567 | map { ref $_ ? $_->[0] : $_ } $self->_order_by_chunks ($rs_attrs->{order_by}) |
568 | } or $self->throw_exception ( |
569 | 'Generic Subquery Limit does not work on resultsets without an order. Provide a single, ' |
570 | . 'unique-column order criteria.' |
571 | ); |
7fca91be |
572 | |
528e717e |
573 | $first_order_by =~ s/\s+ ( ASC|DESC ) \s* $//ix; |
7fca91be |
574 | my $direction = lc ($1 || 'asc'); |
575 | |
528e717e |
576 | my ($first_ord_alias, $first_ord_col) = $first_order_by =~ /^ (?: ([^\.]+) \. )? ([^\.]+) $/x; |
7fca91be |
577 | |
528e717e |
578 | $self->throw_exception(sprintf |
579 | "Generic Subquery Limit order criteria can be only based on the root-source '%s'" |
580 | . " (aliased as '%s')", $root_rsrc->source_name, $rs_attrs->{alias}, |
581 | ) if ($first_ord_alias and $first_ord_alias ne $rs_attrs->{alias}); |
7fca91be |
582 | |
528e717e |
583 | $first_ord_alias ||= $rs_attrs->{alias}; |
7fca91be |
584 | |
70c28808 |
585 | $self->throw_exception( |
528e717e |
586 | "Generic Subquery Limit first order criteria '$first_ord_col' must be unique" |
587 | ) unless $root_rsrc->_identifying_column_set([$first_ord_col]); |
7fca91be |
588 | |
69d3c270 |
589 | my ($stripped_sql, $in_sel, $out_sel, $alias_map, $extra_order_sel) |
590 | = $self->_subqueried_limit_attrs ($sql, $rs_attrs); |
7fca91be |
591 | |
592 | my $cmp_op = $direction eq 'desc' ? '>' : '<'; |
593 | my $count_tbl_alias = 'rownum__emulation'; |
594 | |
595 | my $order_sql = $self->_order_by (delete $rs_attrs->{order_by}); |
596 | my $group_having_sql = $self->_parse_rs_attrs($rs_attrs); |
597 | |
598 | # add the order supplement (if any) as this is what will be used for the outer WHERE |
599 | $in_sel .= ", $_" for keys %{$extra_order_sel||{}}; |
600 | |
69d3c270 |
601 | my $rownum_cond; |
602 | if ($offset) { |
603 | $rownum_cond = 'BETWEEN ? AND ?'; |
604 | |
605 | push @{$self->{limit_bind}}, |
606 | [ $self->__offset_bindtype => $offset ], |
607 | [ $self->__total_bindtype => $offset + $rows - 1] |
608 | ; |
609 | } |
610 | else { |
611 | $rownum_cond = '< ?'; |
612 | |
613 | push @{$self->{limit_bind}}, |
614 | [ $self->__rows_bindtype => $rows ] |
615 | ; |
616 | } |
617 | |
618 | return sprintf (" |
7fca91be |
619 | SELECT $out_sel |
620 | FROM ( |
69d3c270 |
621 | SELECT $in_sel ${stripped_sql}${group_having_sql} |
7fca91be |
622 | ) %s |
69d3c270 |
623 | WHERE ( SELECT COUNT(*) FROM %s %s WHERE %s $cmp_op %s ) $rownum_cond |
7fca91be |
624 | $order_sql |
69d3c270 |
625 | ", map { $self->_quote ($_) } ( |
626 | $rs_attrs->{alias}, |
627 | $root_tbl_name, |
628 | $count_tbl_alias, |
528e717e |
629 | "$count_tbl_alias.$first_ord_col", |
630 | "$first_ord_alias.$first_ord_col", |
69d3c270 |
631 | )); |
7fca91be |
632 | } |
633 | |
634 | |
635 | # !!! THIS IS ALSO HORRIFIC !!! /me ashamed |
636 | # |
637 | # Generates inner/outer select lists for various limit dialects |
638 | # which result in one or more subqueries (e.g. RNO, Top, RowNum) |
639 | # Any non-root-table columns need to have their table qualifier |
640 | # turned into a column alias (otherwise names in subqueries clash |
641 | # and/or lose their source table) |
642 | # |
69d3c270 |
643 | # Returns mangled proto-sql, inner/outer strings of SQL QUOTED selectors |
644 | # with aliases (to be used in whatever select statement), and an alias |
8273e845 |
645 | # index hashref of QUOTED SEL => QUOTED ALIAS pairs (to maybe be used |
69d3c270 |
646 | # for string-subst higher up). |
7fca91be |
647 | # If an order_by is supplied, the inner select needs to bring out columns |
648 | # used in implicit (non-selected) orders, and the order condition itself |
649 | # needs to be realiased to the proper names in the outer query. Thus we |
650 | # also return a hashref (order doesn't matter) of QUOTED EXTRA-SEL => |
651 | # QUOTED ALIAS pairs, which is a list of extra selectors that do *not* |
652 | # exist in the original select list |
7fca91be |
653 | sub _subqueried_limit_attrs { |
69d3c270 |
654 | my ($self, $proto_sql, $rs_attrs) = @_; |
7fca91be |
655 | |
70c28808 |
656 | $self->throw_exception( |
657 | 'Limit dialect implementation usable only in the context of DBIC (missing $rs_attrs)' |
658 | ) unless ref ($rs_attrs) eq 'HASH'; |
7fca91be |
659 | |
f74d22e2 |
660 | # mangle the input sql as we will be replacing the selector entirely |
661 | unless ( |
662 | $rs_attrs->{_selector_sql} |
663 | and |
664 | $proto_sql =~ s/^ \s* SELECT \s* \Q$rs_attrs->{_selector_sql}//ix |
665 | ) { |
666 | $self->throw_exception("Unrecognizable SELECT: $proto_sql"); |
667 | } |
69d3c270 |
668 | |
3f5b99fe |
669 | my ($re_sep, $re_alias) = map { quotemeta $_ } ( $self->{name_sep}, $rs_attrs->{alias} ); |
7fca91be |
670 | |
69d3c270 |
671 | # insulate from the multiple _recurse_fields calls below |
672 | local $self->{select_bind}; |
673 | |
7fca91be |
674 | # correlate select and as, build selection index |
675 | my (@sel, $in_sel_index); |
676 | for my $i (0 .. $#{$rs_attrs->{select}}) { |
677 | |
678 | my $s = $rs_attrs->{select}[$i]; |
679 | my $sql_sel = $self->_recurse_fields ($s); |
680 | my $sql_alias = (ref $s) eq 'HASH' ? $s->{-as} : undef; |
681 | |
7fca91be |
682 | push @sel, { |
683 | sql => $sql_sel, |
69d3c270 |
684 | unquoted_sql => do { |
685 | local $self->{quote_char}; |
686 | $self->_recurse_fields ($s); |
687 | }, |
7fca91be |
688 | as => |
689 | $sql_alias |
690 | || |
691 | $rs_attrs->{as}[$i] |
692 | || |
70c28808 |
693 | $self->throw_exception("Select argument $i ($s) without corresponding 'as'") |
7fca91be |
694 | , |
695 | }; |
696 | |
697 | $in_sel_index->{$sql_sel}++; |
698 | $in_sel_index->{$self->_quote ($sql_alias)}++ if $sql_alias; |
699 | |
700 | # record unqualified versions too, so we do not have |
701 | # to reselect the same column twice (in qualified and |
702 | # unqualified form) |
703 | if (! ref $s && $sql_sel =~ / $re_sep (.+) $/x) { |
704 | $in_sel_index->{$1}++; |
705 | } |
706 | } |
707 | |
708 | |
709 | # re-alias and remove any name separators from aliases, |
710 | # unless we are dealing with the current source alias |
711 | # (which will transcend the subqueries as it is necessary |
712 | # for possible further chaining) |
713 | my (@in_sel, @out_sel, %renamed); |
714 | for my $node (@sel) { |
3f5b99fe |
715 | if ( |
716 | $node->{as} =~ / (?<! ^ $re_alias ) \. /x |
717 | or |
718 | $node->{unquoted_sql} =~ / (?<! ^ $re_alias ) $re_sep /x |
719 | ) { |
7fca91be |
720 | $node->{as} = $self->_unqualify_colname($node->{as}); |
721 | my $quoted_as = $self->_quote($node->{as}); |
722 | push @in_sel, sprintf '%s AS %s', $node->{sql}, $quoted_as; |
723 | push @out_sel, $quoted_as; |
724 | $renamed{$node->{sql}} = $quoted_as; |
725 | } |
726 | else { |
727 | push @in_sel, $node->{sql}; |
728 | push @out_sel, $self->_quote ($node->{as}); |
729 | } |
730 | } |
7fca91be |
731 | # see if the order gives us anything |
732 | my %extra_order_sel; |
733 | for my $chunk ($self->_order_by_chunks ($rs_attrs->{order_by})) { |
734 | # order with bind |
735 | $chunk = $chunk->[0] if (ref $chunk) eq 'ARRAY'; |
736 | $chunk =~ s/\s+ (?: ASC|DESC ) \s* $//ix; |
737 | |
738 | next if $in_sel_index->{$chunk}; |
739 | |
740 | $extra_order_sel{$chunk} ||= $self->_quote ( |
741 | 'ORDER__BY__' . scalar keys %extra_order_sel |
742 | ); |
743 | } |
744 | |
745 | return ( |
69d3c270 |
746 | $proto_sql, |
7fca91be |
747 | (map { join (', ', @$_ ) } ( |
748 | \@in_sel, |
749 | \@out_sel) |
750 | ), |
751 | \%renamed, |
752 | keys %extra_order_sel ? \%extra_order_sel : (), |
753 | ); |
754 | } |
755 | |
756 | sub _unqualify_colname { |
757 | my ($self, $fqcn) = @_; |
3f5b99fe |
758 | $fqcn =~ s/ \. /__/xg; |
7fca91be |
759 | return $fqcn; |
760 | } |
761 | |
762 | 1; |
d5dedbd6 |
763 | |
764 | =head1 AUTHORS |
765 | |
766 | See L<DBIx::Class/CONTRIBUTORS>. |
767 | |
768 | =head1 LICENSE |
769 | |
770 | You may distribute this code under the same terms as Perl itself. |
771 | |
772 | =cut |