1 package DBIx::Class::SQLMaker::LimitDialects;
6 use List::Util 'first';
9 # constants are used not only here, but also in comparison tests
10 sub __rows_bindtype () {
11 +{ sqlt_datatype => 'integer' }
13 sub __offset_bindtype () {
14 +{ sqlt_datatype => 'integer' }
16 sub __total_bindtype () {
17 +{ sqlt_datatype => 'integer' }
22 DBIx::Class::SQLMaker::LimitDialects - SQL::Abstract::Limit-like functionality for DBIx::Class::SQLMaker
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
35 =head1 SQL LIMIT DIALECTS
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
42 Currently the provided dialects are:
46 SELECT ... LIMIT $limit OFFSET $offset
48 Supported by B<PostgreSQL> and B<SQLite>
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 => $rows ];
57 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset ];
64 SELECT ... LIMIT $offset $limit
66 Supported by B<MySQL> and any L<SQL::Statement> based DBD
70 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
71 $sql .= $self->_parse_rs_attrs( $rs_attrs ) . " LIMIT ";
74 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset ];
77 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
85 SELECT *, ROW_NUMBER() OVER( ORDER BY ... ) AS RNO__ROW__INDEX FROM (
88 ) WHERE RNO__ROW__INDEX BETWEEN ($offset+1) AND ($limit+$offset)
91 ANSI standard Limit/Offset implementation. Supported by B<DB2> and
96 my ($self, $sql, $rs_attrs, $rows, $offset ) = @_;
98 # get selectors, and scan the order_by (if any)
99 my $sq_attrs = $self->_subqueried_limit_attrs ( $sql, $rs_attrs );
101 # make up an order if none exists
102 my $requested_order = (delete $rs_attrs->{order_by}) || $self->_rno_default_order;
103 my $rno_ord = $self->_order_by ($requested_order);
105 # this is the order supplement magic
106 my $mid_sel = $sq_attrs->{selection_outer};
107 if (my $extra_order_sel = $sq_attrs->{order_supplement}) {
108 for my $extra_col (sort
109 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
110 keys %$extra_order_sel
112 $sq_attrs->{selection_inner} .= sprintf (', %s AS %s',
114 $extra_order_sel->{$extra_col},
119 # and this is order re-alias magic
120 for ($sq_attrs->{order_supplement}, $sq_attrs->{outer_renames}) {
121 for my $col (keys %$_) {
122 my $re_col = quotemeta ($col);
123 $rno_ord =~ s/$re_col/$_->{$col}/;
127 # whatever is left of the order_by (only where is processed at this point)
128 my $group_having = $self->_parse_rs_attrs($rs_attrs);
130 my $qalias = $self->_quote ($rs_attrs->{alias});
131 my $idx_name = $self->_quote ('rno__row__index');
133 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1], [ $self->__total_bindtype => $offset + $rows ];
137 SELECT $sq_attrs->{selection_outer} FROM (
138 SELECT $mid_sel, ROW_NUMBER() OVER( $rno_ord ) AS $idx_name FROM (
139 SELECT $sq_attrs->{selection_inner} $sq_attrs->{query_leftover}${group_having}
141 ) $qalias WHERE $idx_name >= ? AND $idx_name <= ?
147 # some databases are happy with OVER (), some need OVER (ORDER BY (SELECT (1)) )
148 sub _rno_default_order {
154 SELECT SKIP $offset FIRST $limit * FROM ...
156 Suported by B<Informix>, almost like LimitOffset. According to
157 L<SQL::Abstract::Limit> C<... SKIP $offset LIMIT $limit ...> is also supported.
161 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
163 $sql =~ s/^ \s* SELECT \s+ //ix
164 or $self->throw_exception("Unrecognizable SELECT: $sql");
166 return sprintf ('SELECT %s%s%s%s',
169 push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset];
175 push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ];
179 $self->_parse_rs_attrs ($rs_attrs),
185 SELECT FIRST $limit SKIP $offset * FROM ...
187 Supported by B<Firebird/Interbase>, reverse of SkipFirst. According to
188 L<SQL::Abstract::Limit> C<... ROWS $limit TO $offset ...> is also supported.
192 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
194 $sql =~ s/^ \s* SELECT \s+ //ix
195 or $self->throw_exception("Unrecognizable SELECT: $sql");
197 return sprintf ('SELECT %s%s%s%s',
199 push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ];
204 push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset];
210 $self->_parse_rs_attrs ($rs_attrs),
217 Depending on the resultset attributes one of:
220 SELECT *, ROWNUM rownum__index FROM (
222 ) WHERE ROWNUM <= ($limit+$offset)
223 ) WHERE rownum__index >= ($offset+1)
228 SELECT *, ROWNUM rownum__index FROM (
231 ) WHERE rownum__index BETWEEN ($offset+1) AND ($limit+$offset)
237 ) WHERE ROWNUM <= ($limit+1)
239 Supported by B<Oracle>.
243 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
245 my $sq_attrs = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
247 my $qalias = $self->_quote ($rs_attrs->{alias});
248 my $idx_name = $self->_quote ('rownum__index');
249 my $order_group_having = $self->_parse_rs_attrs($rs_attrs);
252 # if no offset (e.g. first page) - we can skip one of the subqueries
254 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
257 SELECT $sq_attrs->{selection_outer} FROM (
258 SELECT $sq_attrs->{selection_inner} $sq_attrs->{query_leftover}${order_group_having}
259 ) $qalias WHERE ROWNUM <= ?
264 # There are two ways to limit in Oracle, one vastly faster than the other
265 # on large resultsets: https://decipherinfosys.wordpress.com/2007/08/09/paging-and-countstopkey-optimization/
266 # However Oracle is retarded and does not preserve stable ROWNUM() values
267 # when called twice in the same scope. Therefore unless the resultset is
268 # ordered by a unique set of columns, it is not safe to use the faster
269 # method, and the slower BETWEEN query is used instead
271 # FIXME - this is quite expensive, and does not perform caching of any sort
272 # as soon as some of the DQ work becomes viable consider switching this
275 $rs_attrs->{order_by}
277 $rs_attrs->{_rsroot_rsrc}->storage->_order_by_is_stable(
278 $rs_attrs->{from}, $rs_attrs->{order_by}
281 push @{$self->{limit_bind}}, [ $self->__total_bindtype => $offset + $rows ], [ $self->__offset_bindtype => $offset + 1 ];
284 SELECT $sq_attrs->{selection_outer} FROM (
285 SELECT $sq_attrs->{selection_outer}, ROWNUM $idx_name FROM (
286 SELECT $sq_attrs->{selection_inner} $sq_attrs->{query_leftover}${order_group_having}
287 ) $qalias WHERE ROWNUM <= ?
288 ) $qalias WHERE $idx_name >= ?
292 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1 ], [ $self->__total_bindtype => $offset + $rows ];
295 SELECT $sq_attrs->{selection_outer} FROM (
296 SELECT $sq_attrs->{selection_outer}, ROWNUM $idx_name FROM (
297 SELECT $sq_attrs->{selection_inner} $sq_attrs->{query_leftover}${order_group_having}
299 ) $qalias WHERE $idx_name BETWEEN ? AND ?
304 # used by _Top and _FetchFirst below
305 sub _prep_for_skimming_limit {
306 my ( $self, $sql, $rs_attrs ) = @_;
309 my $sq_attrs = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
311 my $requested_order = delete $rs_attrs->{order_by};
312 $sq_attrs->{order_by_requested} = $self->_order_by ($requested_order);
313 $sq_attrs->{grpby_having} = $self->_parse_rs_attrs ($rs_attrs);
315 # make up an order unless supplied or sanity check what we are given
317 if ($sq_attrs->{order_by_requested}) {
318 $self->throw_exception (
319 'Unable to safely perform "skimming type" limit with supplied unstable order criteria'
320 ) unless $rs_attrs->{_rsroot_rsrc}->schema->storage->_order_by_is_stable(
325 $inner_order = $requested_order;
329 { "$rs_attrs->{alias}.$_" }
331 $rs_attrs->{_rsroot_rsrc}->_identifying_column_set
333 $self->throw_exception(sprintf(
334 'Unable to auto-construct stable order criteria for "skimming type" limit '
335 . "dialect based on source '%s'", $rs_attrs->{_rsroot_rsrc}->name) );
340 # localise as we already have all the bind values we need
341 local $self->{order_bind};
343 $sq_attrs->{order_by_inner} = $self->_order_by ($inner_order);
346 for my $ch ($self->_order_by_chunks ($inner_order)) {
347 $ch = $ch->[0] if ref $ch eq 'ARRAY';
349 $ch =~ s/\s+ ( ASC|DESC ) \s* $//ix;
350 my $dir = uc ($1||'ASC');
352 push @out_chunks, \join (' ', $ch, $dir eq 'ASC' ? 'DESC' : 'ASC' );
355 $sq_attrs->{quoted_rs_alias} = $self->_quote ($rs_attrs->{alias});
356 $sq_attrs->{order_by_middle} = $self->_order_by (\@out_chunks);
357 $sq_attrs->{selection_middle} = $sq_attrs->{selection_outer};
359 # this is the order supplement magic
360 if (my $extra_order_sel = $sq_attrs->{order_supplement}) {
361 for my $extra_col (sort
362 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
363 keys %$extra_order_sel
365 $sq_attrs->{selection_inner} .= sprintf (', %s AS %s',
367 $extra_order_sel->{$extra_col},
370 $sq_attrs->{selection_middle} .= ', ' . $extra_order_sel->{$extra_col};
373 # Whatever order bindvals there are, they will be realiased and
374 # reselected, and need to show up at end of the initial inner select
375 push @{$self->{select_bind}}, @{$self->{order_bind}};
377 # if this is a part of something bigger, we need to add back all
378 # the extra order_by's, as they may be relied upon by the outside
379 # of a prefetch or something
380 if ($rs_attrs->{_is_internal_subuery}) {
381 $sq_attrs->{selection_outer} .= sprintf ", $extra_order_sel->{$_} AS $_"
383 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
384 grep { $_ !~ /[^\w\-]/ } # ignore functions
385 keys %$extra_order_sel
390 # and this is order re-alias magic
391 for my $map ($sq_attrs->{order_supplement}, $sq_attrs->{outer_renames}) {
392 for my $col (sort { $map->{$a} cmp $map->{$b} } keys %{$map||{}}) {
393 my $re_col = quotemeta ($col);
394 $_ =~ s/$re_col/$map->{$col}/
395 for ($sq_attrs->{order_by_middle}, $sq_attrs->{order_by_requested});
406 SELECT TOP $limit FROM (
407 SELECT TOP $limit FROM (
408 SELECT TOP ($limit+$offset) ...
409 ) ORDER BY $reversed_original_order
410 ) ORDER BY $original_order
412 Unreliable Top-based implementation, supported by B<< MSSQL < 2005 >>.
416 Due to its implementation, this limit dialect returns B<incorrect results>
417 when $limit+$offset > total amount of rows in the resultset.
422 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
424 my $lim = $self->_prep_for_skimming_limit($sql, $rs_attrs);
426 $sql = sprintf ('SELECT TOP %u %s %s %s %s',
427 $rows + ($offset||0),
428 $lim->{selection_inner},
429 $lim->{query_leftover},
430 $lim->{grpby_having},
431 $lim->{order_by_inner},
434 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
436 $lim->{selection_middle},
438 $lim->{quoted_rs_alias},
439 $lim->{order_by_middle},
442 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
444 $lim->{selection_outer},
446 $lim->{quoted_rs_alias},
447 $lim->{order_by_requested},
449 $lim->{order_by_requested} or $lim->{selection_middle} ne $lim->{selection_outer}
462 ) ORDER BY $reversed_original_order
463 FETCH FIRST $limit ROWS ONLY
464 ) ORDER BY $original_order
465 FETCH FIRST $limit ROWS ONLY
468 Unreliable FetchFirst-based implementation, supported by B<< IBM DB2 <= V5R3 >>.
472 Due to its implementation, this limit dialect returns B<incorrect results>
473 when $limit+$offset > total amount of rows in the resultset.
478 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
480 my $lim = $self->_prep_for_skimming_limit($sql, $rs_attrs);
482 $sql = sprintf ('SELECT %s %s %s %s FETCH FIRST %u ROWS ONLY',
483 $lim->{selection_inner},
484 $lim->{query_leftover},
485 $lim->{grpby_having},
486 $lim->{order_by_inner},
487 $rows + ($offset||0),
490 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
491 $lim->{selection_middle},
493 $lim->{quoted_rs_alias},
494 $lim->{order_by_middle},
499 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
500 $lim->{selection_outer},
502 $lim->{quoted_rs_alias},
503 $lim->{order_by_requested},
506 $lim->{order_by_requested} or $lim->{selection_middle} ne $lim->{selection_outer}
512 =head2 RowCountOrGenericSubQ
514 This is not exactly a limit dialect, but more of a proxy for B<Sybase ASE>.
515 If no $offset is supplied the limit is simply performed as:
521 Otherwise we fall back to L</GenericSubQ>
525 sub _RowCountOrGenericSubQ {
527 my ($sql, $rs_attrs, $rows, $offset) = @_;
529 return $self->_GenericSubQ(@_) if $offset;
531 return sprintf <<"EOF", $rows, $sql;
544 SELECT COUNT(*) FROM $original_table cnt WHERE cnt.id < $original_table.id
545 ) BETWEEN $offset AND ($offset+$rows-1)
547 This is the most evil limit "dialect" (more of a hack) for I<really> stupid
548 databases. It works by ordering the set by some unique column, and calculating
549 the amount of rows that have a less-er value (thus emulating a L</RowNum>-like
550 index). Of course this implies the set can only be ordered by a single unique
551 column. Also note that this technique can be and often is B<excruciatingly
554 Currently used by B<Sybase ASE>, due to lack of any other option.
558 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
560 my $root_rsrc = $rs_attrs->{_rsroot_rsrc};
561 my $root_tbl_name = $root_rsrc->name;
563 my ($first_order_by) = do {
564 local $self->{quote_char};
565 map { ref $_ ? $_->[0] : $_ } $self->_order_by_chunks ($rs_attrs->{order_by})
566 } or $self->throw_exception (
567 'Generic Subquery Limit does not work on resultsets without an order. Provide a single, '
568 . 'unique-column order criteria.'
571 $first_order_by =~ s/\s+ ( ASC|DESC ) \s* $//ix;
572 my $direction = lc ($1 || 'asc');
574 my ($first_ord_alias, $first_ord_col) = $first_order_by =~ /^ (?: ([^\.]+) \. )? ([^\.]+) $/x;
576 $self->throw_exception(sprintf
577 "Generic Subquery Limit order criteria can be only based on the root-source '%s'"
578 . " (aliased as '%s')", $root_rsrc->source_name, $rs_attrs->{alias},
579 ) if ($first_ord_alias and $first_ord_alias ne $rs_attrs->{alias});
581 $first_ord_alias ||= $rs_attrs->{alias};
583 $self->throw_exception(
584 "Generic Subquery Limit first order criteria '$first_ord_col' must be unique"
585 ) unless $root_rsrc->_identifying_column_set([$first_ord_col]);
587 my $sq_attrs = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
589 my $cmp_op = $direction eq 'desc' ? '>' : '<';
590 my $count_tbl_alias = 'rownum__emulation';
592 my $order_sql = $self->_order_by (delete $rs_attrs->{order_by});
593 my $group_having_sql = $self->_parse_rs_attrs($rs_attrs);
595 my $in_sel = $sq_attrs->{selection_inner};
597 # add the order supplement (if any) as this is what will be used for the outer WHERE
598 $in_sel .= ", $_" for keys %{$sq_attrs->{order_supplement}};
602 $rownum_cond = 'BETWEEN ? AND ?';
604 push @{$self->{limit_bind}},
605 [ $self->__offset_bindtype => $offset ],
606 [ $self->__total_bindtype => $offset + $rows - 1]
610 $rownum_cond = '< ?';
612 push @{$self->{limit_bind}},
613 [ $self->__rows_bindtype => $rows ]
618 SELECT $sq_attrs->{selection_outer}
620 SELECT $in_sel $sq_attrs->{query_leftover}${group_having_sql}
622 WHERE ( SELECT COUNT(*) FROM %s %s WHERE %s $cmp_op %s ) $rownum_cond
624 ", map { $self->_quote ($_) } (
628 "$count_tbl_alias.$first_ord_col",
629 "$first_ord_alias.$first_ord_col",
634 # !!! THIS IS ALSO HORRIFIC !!! /me ashamed
636 # Generates inner/outer select lists for various limit dialects
637 # which result in one or more subqueries (e.g. RNO, Top, RowNum)
638 # Any non-root-table columns need to have their table qualifier
639 # turned into a column alias (otherwise names in subqueries clash
640 # and/or lose their source table)
642 # Returns mangled proto-sql, inner/outer strings of SQL QUOTED selectors
643 # with aliases (to be used in whatever select statement), and an alias
644 # index hashref of QUOTED SEL => QUOTED ALIAS pairs (to maybe be used
645 # for string-subst higher up).
646 # If an order_by is supplied, the inner select needs to bring out columns
647 # used in implicit (non-selected) orders, and the order condition itself
648 # needs to be realiased to the proper names in the outer query. Thus we
649 # also return a hashref (order doesn't matter) of QUOTED EXTRA-SEL =>
650 # QUOTED ALIAS pairs, which is a list of extra selectors that do *not*
651 # exist in the original select list
652 sub _subqueried_limit_attrs {
653 my ($self, $proto_sql, $rs_attrs) = @_;
655 $self->throw_exception(
656 'Limit dialect implementation usable only in the context of DBIC (missing $rs_attrs)'
657 ) unless ref ($rs_attrs) eq 'HASH';
659 # mangle the input sql as we will be replacing the selector entirely
661 $rs_attrs->{_selector_sql}
663 $proto_sql =~ s/^ \s* SELECT \s* \Q$rs_attrs->{_selector_sql}//ix
665 $self->throw_exception("Unrecognizable SELECT: $proto_sql");
668 my ($re_sep, $re_alias) = map { quotemeta $_ } ( $self->{name_sep}, $rs_attrs->{alias} );
670 # insulate from the multiple _recurse_fields calls below
671 local $self->{select_bind};
673 # correlate select and as, build selection index
674 my (@sel, $in_sel_index);
675 for my $i (0 .. $#{$rs_attrs->{select}}) {
677 my $s = $rs_attrs->{select}[$i];
678 my $sql_sel = $self->_recurse_fields ($s);
679 my $sql_alias = (ref $s) eq 'HASH' ? $s->{-as} : undef;
684 local $self->{quote_char};
685 $self->_recurse_fields ($s);
692 $self->throw_exception("Select argument $i ($s) without corresponding 'as'")
696 $in_sel_index->{$sql_sel}++;
697 $in_sel_index->{$self->_quote ($sql_alias)}++ if $sql_alias;
699 # record unqualified versions too, so we do not have
700 # to reselect the same column twice (in qualified and
702 if (! ref $s && $sql_sel =~ / $re_sep (.+) $/x) {
703 $in_sel_index->{$1}++;
708 # re-alias and remove any name separators from aliases,
709 # unless we are dealing with the current source alias
710 # (which will transcend the subqueries as it is necessary
711 # for possible further chaining)
713 for my $node (@sel) {
715 $node->{as} =~ / (?<! ^ $re_alias ) \. /x
717 $node->{unquoted_sql} =~ / (?<! ^ $re_alias ) $re_sep /x
719 $node->{as} = $self->_unqualify_colname($node->{as});
720 my $quoted_as = $self->_quote($node->{as});
721 push @{$sel->{inner}}, sprintf '%s AS %s', $node->{sql}, $quoted_as;
722 push @{$sel->{outer}}, $quoted_as;
723 $renamed->{$node->{sql}} = $quoted_as;
726 push @{$sel->{inner}}, $node->{sql};
727 push @{$sel->{outer}}, $self->_quote ($node->{as});
731 # see if the order gives us anything
733 for my $chunk ($self->_order_by_chunks ($rs_attrs->{order_by})) {
735 $chunk = $chunk->[0] if (ref $chunk) eq 'ARRAY';
736 $chunk =~ s/\s+ (?: ASC|DESC ) \s* $//ix;
738 next if $in_sel_index->{$chunk};
740 $extra_order_sel->{$chunk} ||= $self->_quote (
741 'ORDER__BY__' . scalar keys %{$extra_order_sel||{}}
746 query_leftover => $proto_sql,
747 (map {( "selection_$_" => join (', ', @{$sel->{$_}} ) )} keys %$sel ),
748 outer_renames => $renamed,
749 order_supplement => $extra_order_sel,
753 sub _unqualify_colname {
754 my ($self, $fqcn) = @_;
755 $fqcn =~ s/ \. /__/xg;
763 See L<DBIx::Class/CONTRIBUTORS>.
767 You may distribute this code under the same terms as Perl itself.