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;
104 # the order binds (if any) will need to go at the end of the entire inner select
105 local $self->{order_bind};
106 my $rno_ord = $self->_order_by ($requested_order);
107 push @{$self->{select_bind}}, @{$self->{order_bind}};
109 # this is the order supplement magic
110 my $mid_sel = $sq_attrs->{selection_outer};
111 if (my $extra_order_sel = $sq_attrs->{order_supplement}) {
112 for my $extra_col (sort
113 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
114 keys %$extra_order_sel
116 $sq_attrs->{selection_inner} .= sprintf (', %s AS %s',
118 $extra_order_sel->{$extra_col},
123 # and this is order re-alias magic
124 for my $map ($sq_attrs->{order_supplement}, $sq_attrs->{outer_renames}) {
125 for my $col (sort { (length $b) <=> (length $a) } keys %{$map||{}} ) {
126 my $re_col = quotemeta ($col);
127 $rno_ord =~ s/$re_col/$map->{$col}/;
131 # whatever is left of the order_by (only where is processed at this point)
132 my $group_having = $self->_parse_rs_attrs($rs_attrs);
134 my $qalias = $self->_quote ($rs_attrs->{alias});
135 my $idx_name = $self->_quote ('rno__row__index');
137 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1], [ $self->__total_bindtype => $offset + $rows ];
141 SELECT $sq_attrs->{selection_outer} FROM (
142 SELECT $mid_sel, ROW_NUMBER() OVER( $rno_ord ) AS $idx_name FROM (
143 SELECT $sq_attrs->{selection_inner} $sq_attrs->{query_leftover}${group_having}
145 ) $qalias WHERE $idx_name >= ? AND $idx_name <= ?
151 # some databases are happy with OVER (), some need OVER (ORDER BY (SELECT (1)) )
152 sub _rno_default_order {
158 SELECT SKIP $offset FIRST $limit * FROM ...
160 Suported by B<Informix>, almost like LimitOffset. According to
161 L<SQL::Abstract::Limit> C<... SKIP $offset LIMIT $limit ...> is also supported.
165 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
167 $sql =~ s/^ \s* SELECT \s+ //ix
168 or $self->throw_exception("Unrecognizable SELECT: $sql");
170 return sprintf ('SELECT %s%s%s%s',
173 push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset];
179 push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ];
183 $self->_parse_rs_attrs ($rs_attrs),
189 SELECT FIRST $limit SKIP $offset * FROM ...
191 Supported by B<Firebird/Interbase>, reverse of SkipFirst. According to
192 L<SQL::Abstract::Limit> C<... ROWS $limit TO $offset ...> is also supported.
196 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
198 $sql =~ s/^ \s* SELECT \s+ //ix
199 or $self->throw_exception("Unrecognizable SELECT: $sql");
201 return sprintf ('SELECT %s%s%s%s',
203 push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ];
208 push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset];
214 $self->_parse_rs_attrs ($rs_attrs),
221 Depending on the resultset attributes one of:
224 SELECT *, ROWNUM rownum__index FROM (
226 ) WHERE ROWNUM <= ($limit+$offset)
227 ) WHERE rownum__index >= ($offset+1)
232 SELECT *, ROWNUM rownum__index FROM (
235 ) WHERE rownum__index BETWEEN ($offset+1) AND ($limit+$offset)
241 ) WHERE ROWNUM <= ($limit+1)
243 Supported by B<Oracle>.
247 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
249 my $sq_attrs = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
251 my $qalias = $self->_quote ($rs_attrs->{alias});
252 my $idx_name = $self->_quote ('rownum__index');
253 my $order_group_having = $self->_parse_rs_attrs($rs_attrs);
256 # if no offset (e.g. first page) - we can skip one of the subqueries
258 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
261 SELECT $sq_attrs->{selection_outer} FROM (
262 SELECT $sq_attrs->{selection_inner} $sq_attrs->{query_leftover}${order_group_having}
263 ) $qalias WHERE ROWNUM <= ?
268 # There are two ways to limit in Oracle, one vastly faster than the other
269 # on large resultsets: https://decipherinfosys.wordpress.com/2007/08/09/paging-and-countstopkey-optimization/
270 # However Oracle is retarded and does not preserve stable ROWNUM() values
271 # when called twice in the same scope. Therefore unless the resultset is
272 # ordered by a unique set of columns, it is not safe to use the faster
273 # method, and the slower BETWEEN query is used instead
275 # FIXME - this is quite expensive, and does not perform caching of any sort
276 # as soon as some of the DQ work becomes viable consider switching this
279 $rs_attrs->{order_by}
281 $rs_attrs->{_rsroot_rsrc}->storage->_order_by_is_stable(
282 @{$rs_attrs}{qw/from order_by where/}
285 push @{$self->{limit_bind}}, [ $self->__total_bindtype => $offset + $rows ], [ $self->__offset_bindtype => $offset + 1 ];
288 SELECT $sq_attrs->{selection_outer} FROM (
289 SELECT $sq_attrs->{selection_outer}, ROWNUM $idx_name FROM (
290 SELECT $sq_attrs->{selection_inner} $sq_attrs->{query_leftover}${order_group_having}
291 ) $qalias WHERE ROWNUM <= ?
292 ) $qalias WHERE $idx_name >= ?
296 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1 ], [ $self->__total_bindtype => $offset + $rows ];
299 SELECT $sq_attrs->{selection_outer} FROM (
300 SELECT $sq_attrs->{selection_outer}, ROWNUM $idx_name FROM (
301 SELECT $sq_attrs->{selection_inner} $sq_attrs->{query_leftover}${order_group_having}
303 ) $qalias WHERE $idx_name BETWEEN ? AND ?
308 # used by _Top and _FetchFirst below
309 sub _prep_for_skimming_limit {
310 my ( $self, $sql, $rs_attrs ) = @_;
313 my $sq_attrs = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
315 my $requested_order = delete $rs_attrs->{order_by};
316 $sq_attrs->{order_by_requested} = $self->_order_by ($requested_order);
317 $sq_attrs->{grpby_having} = $self->_parse_rs_attrs ($rs_attrs);
319 # without an offset things are easy
320 if (! $rs_attrs->{offset}) {
321 $sq_attrs->{order_by_inner} = $sq_attrs->{order_by_requested};
324 $sq_attrs->{quoted_rs_alias} = $self->_quote ($rs_attrs->{alias});
326 # localise as we already have all the bind values we need
327 local $self->{order_bind};
329 # make up an order unless supplied or sanity check what we are given
331 if ($sq_attrs->{order_by_requested}) {
332 $self->throw_exception (
333 'Unable to safely perform "skimming type" limit with supplied unstable order criteria'
334 ) unless ($rs_attrs->{_rsroot_rsrc}->schema->storage->_order_by_is_stable(
340 $inner_order = $requested_order;
344 { "$rs_attrs->{alias}.$_" }
346 $rs_attrs->{_rsroot_rsrc}->_identifying_column_set
348 $self->throw_exception(sprintf(
349 'Unable to auto-construct stable order criteria for "skimming type" limit '
350 . "dialect based on source '%s'", $rs_attrs->{_rsroot_rsrc}->name) );
355 $sq_attrs->{order_by_inner} = $self->_order_by ($inner_order);
358 for my $ch ($self->_order_by_chunks ($inner_order)) {
359 $ch = $ch->[0] if ref $ch eq 'ARRAY';
362 $ch =~ s/\s+ ( ASC|DESC ) \s* $//ix
366 push @out_chunks, \join (' ', $ch, $is_desc ? 'ASC' : 'DESC' );
369 $sq_attrs->{order_by_middle} = $self->_order_by (\@out_chunks);
371 # this is the order supplement magic
372 $sq_attrs->{selection_middle} = $sq_attrs->{selection_outer};
373 if (my $extra_order_sel = $sq_attrs->{order_supplement}) {
374 for my $extra_col (sort
375 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
376 keys %$extra_order_sel
378 $sq_attrs->{selection_inner} .= sprintf (', %s AS %s',
380 $extra_order_sel->{$extra_col},
383 $sq_attrs->{selection_middle} .= ', ' . $extra_order_sel->{$extra_col};
386 # Whatever order bindvals there are, they will be realiased and
387 # reselected, and need to show up at end of the initial inner select
388 push @{$self->{select_bind}}, @{$self->{order_bind}};
391 # and this is order re-alias magic
392 for my $map ($sq_attrs->{order_supplement}, $sq_attrs->{outer_renames}) {
393 for my $col (sort { (length $b) <=> (length $a) } keys %{$map||{}}) {
394 my $re_col = quotemeta ($col);
395 $_ =~ s/$re_col/$map->{$col}/
396 for ($sq_attrs->{order_by_middle}, $sq_attrs->{order_by_requested});
408 SELECT TOP $limit FROM (
409 SELECT TOP $limit FROM (
410 SELECT TOP ($limit+$offset) ...
411 ) ORDER BY $reversed_original_order
412 ) ORDER BY $original_order
414 Unreliable Top-based implementation, supported by B<< MSSQL < 2005 >>.
418 Due to its implementation, this limit dialect returns B<incorrect results>
419 when $limit+$offset > total amount of rows in the resultset.
424 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
426 my $lim = $self->_prep_for_skimming_limit($sql, $rs_attrs);
428 $sql = sprintf ('SELECT TOP %u %s %s %s %s',
429 $rows + ($offset||0),
430 $offset ? $lim->{selection_inner} : $lim->{selection_original},
431 $lim->{query_leftover},
432 $lim->{grpby_having},
433 $lim->{order_by_inner},
436 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
438 $lim->{selection_middle},
440 $lim->{quoted_rs_alias},
441 $lim->{order_by_middle},
444 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s',
445 $lim->{selection_outer},
447 $lim->{quoted_rs_alias},
448 $lim->{order_by_requested},
450 $lim->{order_by_requested} or $lim->{selection_middle} ne $lim->{selection_outer}
463 ) ORDER BY $reversed_original_order
464 FETCH FIRST $limit ROWS ONLY
465 ) ORDER BY $original_order
466 FETCH FIRST $limit ROWS ONLY
469 Unreliable FetchFirst-based implementation, supported by B<< IBM DB2 <= V5R3 >>.
473 Due to its implementation, this limit dialect returns B<incorrect results>
474 when $limit+$offset > total amount of rows in the resultset.
479 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
481 my $lim = $self->_prep_for_skimming_limit($sql, $rs_attrs);
483 $sql = sprintf ('SELECT %s %s %s %s FETCH FIRST %u ROWS ONLY',
484 $offset ? $lim->{selection_inner} : $lim->{selection_original},
485 $lim->{query_leftover},
486 $lim->{grpby_having},
487 $lim->{order_by_inner},
488 $rows + ($offset||0),
491 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
492 $lim->{selection_middle},
494 $lim->{quoted_rs_alias},
495 $lim->{order_by_middle},
500 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s',
501 $lim->{selection_outer},
503 $lim->{quoted_rs_alias},
504 $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, $self->_parse_rs_attrs( $rs_attrs );
544 SELECT COUNT(*) FROM $original_table cnt WHERE cnt.id < $original_table.id
545 ) BETWEEN $offset AND ($offset+$rows-1)
547 This is the most evil limit "dialect" (more of a hack) for I<really> stupid
548 databases. It works by ordering the set by some unique column, and calculating
549 the amount of rows that have a less-er value (thus emulating a L</RowNum>-like
550 index). Of course this implies the set can only be ordered by a single unique
553 Also note that this technique can be and often is B<excruciatingly slow>. You
554 may have much better luck using L<DBIx::Class::ResultSet/software_limit>
557 Currently used by B<Sybase ASE>, due to lack of any other option.
561 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
563 my $root_rsrc = $rs_attrs->{_rsroot_rsrc};
564 my $root_tbl_name = $root_rsrc->name;
566 my ($first_order_by) = do {
567 local $self->{quote_char};
568 local $self->{order_bind};
569 map { ref $_ ? $_->[0] : $_ } $self->_order_by_chunks ($rs_attrs->{order_by})
570 } or $self->throw_exception (
571 'Generic Subquery Limit does not work on resultsets without an order. Provide a single, '
572 . 'unique-column order criteria.'
576 $first_order_by =~ s/\s+ ( ASC|DESC ) \s* $//ix
579 my ($first_ord_alias, $first_ord_col) = $first_order_by =~ /^ (?: ([^\.]+) \. )? ([^\.]+) $/x;
581 $self->throw_exception(sprintf
582 "Generic Subquery Limit order criteria can be only based on the root-source '%s'"
583 . " (aliased as '%s')", $root_rsrc->source_name, $rs_attrs->{alias},
584 ) if ($first_ord_alias and $first_ord_alias ne $rs_attrs->{alias});
586 $first_ord_alias ||= $rs_attrs->{alias};
588 $self->throw_exception(
589 "Generic Subquery Limit first order criteria '$first_ord_col' must be unique"
590 ) unless $root_rsrc->_identifying_column_set([$first_ord_col]);
593 # perform the mangling only using the very first order crietria
594 # (the one we care about)
595 local $rs_attrs->{order_by} = $first_order_by;
596 $self->_subqueried_limit_attrs ($sql, $rs_attrs);
599 my $cmp_op = $direction eq 'desc' ? '>' : '<';
600 my $count_tbl_alias = 'rownum__emulation';
602 my ($order_sql, @order_bind) = do {
603 local $self->{order_bind};
604 my $s = $self->_order_by (delete $rs_attrs->{order_by});
605 ($s, @{$self->{order_bind}});
607 my $group_having_sql = $self->_parse_rs_attrs($rs_attrs);
609 my $in_sel = $sq_attrs->{selection_inner};
611 # add the order supplement (if any) as this is what will be used for the outer WHERE
612 $in_sel .= ", $_" for keys %{$sq_attrs->{order_supplement}};
616 $rownum_cond = 'BETWEEN ? AND ?';
618 push @{$self->{limit_bind}},
619 [ $self->__offset_bindtype => $offset ],
620 [ $self->__total_bindtype => $offset + $rows - 1]
624 $rownum_cond = '< ?';
626 push @{$self->{limit_bind}},
627 [ $self->__rows_bindtype => $rows ]
631 # even though binds in order_by make no sense here (the rs needs to be
632 # ordered by a unique column first) - pass whatever there may be through
634 push @{$self->{limit_bind}}, @order_bind;
637 SELECT $sq_attrs->{selection_outer}
639 SELECT $in_sel $sq_attrs->{query_leftover}${group_having_sql}
641 WHERE ( SELECT COUNT(*) FROM %s %s WHERE %s $cmp_op %s ) $rownum_cond
643 ", map { $self->_quote ($_) } (
647 "$count_tbl_alias.$first_ord_col",
648 "$first_ord_alias.$first_ord_col",
653 # !!! THIS IS ALSO HORRIFIC !!! /me ashamed
655 # Generates inner/outer select lists for various limit dialects
656 # which result in one or more subqueries (e.g. RNO, Top, RowNum)
657 # Any non-root-table columns need to have their table qualifier
658 # turned into a column alias (otherwise names in subqueries clash
659 # and/or lose their source table)
661 # Returns mangled proto-sql, inner/outer strings of SQL QUOTED selectors
662 # with aliases (to be used in whatever select statement), and an alias
663 # index hashref of QUOTED SEL => QUOTED ALIAS pairs (to maybe be used
664 # for string-subst higher up).
665 # If an order_by is supplied, the inner select needs to bring out columns
666 # used in implicit (non-selected) orders, and the order condition itself
667 # needs to be realiased to the proper names in the outer query. Thus we
668 # also return a hashref (order doesn't matter) of QUOTED EXTRA-SEL =>
669 # QUOTED ALIAS pairs, which is a list of extra selectors that do *not*
670 # exist in the original select list
671 sub _subqueried_limit_attrs {
672 my ($self, $proto_sql, $rs_attrs) = @_;
674 $self->throw_exception(
675 'Limit dialect implementation usable only in the context of DBIC (missing $rs_attrs)'
676 ) unless ref ($rs_attrs) eq 'HASH';
678 # mangle the input sql as we will be replacing the selector entirely
680 $rs_attrs->{_selector_sql}
682 $proto_sql =~ s/^ \s* SELECT \s* \Q$rs_attrs->{_selector_sql}//ix
684 $self->throw_exception("Unrecognizable SELECT: $proto_sql");
687 my ($re_sep, $re_alias) = map { quotemeta $_ } ( $self->{name_sep}, $rs_attrs->{alias} );
689 # insulate from the multiple _recurse_fields calls below
690 local $self->{select_bind};
692 # correlate select and as, build selection index
693 my (@sel, $in_sel_index);
694 for my $i (0 .. $#{$rs_attrs->{select}}) {
696 my $s = $rs_attrs->{select}[$i];
697 my $sql_sel = $self->_recurse_fields ($s);
698 my $sql_alias = (ref $s) eq 'HASH' ? $s->{-as} : undef;
704 local $self->{quote_char};
705 $self->_recurse_fields ($s);
712 $self->throw_exception("Select argument $i ($s) without corresponding 'as'")
716 # anything with a placeholder in it needs re-selection
717 $in_sel_index->{$sql_sel}++ unless $sql_sel =~ / (?: ^ | \W ) \? (?: \W | $ ) /x;
719 $in_sel_index->{$self->_quote ($sql_alias)}++ if $sql_alias;
721 # record unqualified versions too, so we do not have
722 # to reselect the same column twice (in qualified and
724 if (! ref $s && $sql_sel =~ / $re_sep (.+) $/x) {
725 $in_sel_index->{$1}++;
730 # re-alias and remove any name separators from aliases,
731 # unless we are dealing with the current source alias
732 # (which will transcend the subqueries as it is necessary
733 # for possible further chaining)
734 # same for anything we do not recognize
736 for my $node (@sel) {
737 push @{$sel->{original}}, $node->{sql};
740 ! $in_sel_index->{$node->{sql}}
742 $node->{as} =~ / (?<! ^ $re_alias ) \. /x
744 $node->{unquoted_sql} =~ / (?<! ^ $re_alias ) $re_sep /x
746 $node->{as} = $self->_unqualify_colname($node->{as});
747 my $quoted_as = $self->_quote($node->{as});
748 push @{$sel->{inner}}, sprintf '%s AS %s', $node->{sql}, $quoted_as;
749 push @{$sel->{outer}}, $quoted_as;
750 $renamed->{$node->{sql}} = $quoted_as;
753 push @{$sel->{inner}}, $node->{sql};
754 push @{$sel->{outer}}, $self->_quote (ref $node->{arg} ? $node->{as} : $node->{arg});
758 # see if the order gives us anything
760 for my $chunk ($self->_order_by_chunks ($rs_attrs->{order_by})) {
762 $chunk = $chunk->[0] if (ref $chunk) eq 'ARRAY';
763 $chunk =~ s/\s+ (?: ASC|DESC ) \s* $//ix;
765 next if $in_sel_index->{$chunk};
767 $extra_order_sel->{$chunk} ||= $self->_quote (
768 'ORDER__BY__' . sprintf '%03d', scalar keys %{$extra_order_sel||{}}
773 query_leftover => $proto_sql,
774 (map {( "selection_$_" => join (', ', @{$sel->{$_}} ) )} keys %$sel ),
775 outer_renames => $renamed,
776 order_supplement => $extra_order_sel,
780 sub _unqualify_colname {
781 my ($self, $fqcn) = @_;
782 $fqcn =~ s/ \. /__/xg;
790 See L<DBIx::Class/CONTRIBUTORS>.
794 You may distribute this code under the same terms as Perl itself.