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 # mangle the input sql as we will be replacing the selector
99 $sql =~ s/^ \s* SELECT \s+ .+? \s+ (?= \b FROM \b )//ix
100 or $self->throw_exception("Unrecognizable SELECT: $sql");
102 # get selectors, and scan the order_by (if any)
103 my ($in_sel, $out_sel, $alias_map, $extra_order_sel)
104 = $self->_subqueried_limit_attrs ( $rs_attrs );
106 # make up an order if none exists
107 my $requested_order = (delete $rs_attrs->{order_by}) || $self->_rno_default_order;
108 my $rno_ord = $self->_order_by ($requested_order);
110 # this is the order supplement magic
111 my $mid_sel = $out_sel;
112 if ($extra_order_sel) {
113 for my $extra_col (sort
114 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
115 keys %$extra_order_sel
117 $in_sel .= sprintf (', %s AS %s',
119 $extra_order_sel->{$extra_col},
122 $mid_sel .= ', ' . $extra_order_sel->{$extra_col};
126 # and this is order re-alias magic
127 for ($extra_order_sel, $alias_map) {
128 for my $col (keys %$_) {
129 my $re_col = quotemeta ($col);
130 $rno_ord =~ s/$re_col/$_->{$col}/;
134 # whatever is left of the order_by (only where is processed at this point)
135 my $group_having = $self->_parse_rs_attrs($rs_attrs);
137 my $qalias = $self->_quote ($rs_attrs->{alias});
138 my $idx_name = $self->_quote ('rno__row__index');
142 SELECT $out_sel FROM (
143 SELECT $mid_sel, ROW_NUMBER() OVER( $rno_ord ) AS $idx_name FROM (
144 SELECT $in_sel ${sql}${group_having}
146 ) $qalias WHERE $idx_name >= ? AND $idx_name <= ?
149 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1], [ $self->__total_bindtype => $offset + $rows ];
154 # some databases are happy with OVER (), some need OVER (ORDER BY (SELECT (1)) )
155 sub _rno_default_order {
161 SELECT SKIP $offset FIRST $limit * FROM ...
163 Suported by B<Informix>, almost like LimitOffset. According to
164 L<SQL::Abstract::Limit> C<... SKIP $offset LIMIT $limit ...> is also supported.
168 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
170 $sql =~ s/^ \s* SELECT \s+ //ix
171 or $self->throw_exception("Unrecognizable SELECT: $sql");
173 return sprintf ('SELECT %s%s%s%s',
176 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset];
182 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
186 $self->_parse_rs_attrs ($rs_attrs),
192 SELECT FIRST $limit SKIP $offset * FROM ...
194 Supported by B<Firebird/Interbase>, reverse of SkipFirst. According to
195 L<SQL::Abstract::Limit> C<... ROWS $limit TO $offset ...> is also supported.
199 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
201 $sql =~ s/^ \s* SELECT \s+ //ix
202 or $self->throw_exception("Unrecognizable SELECT: $sql");
204 return sprintf ('SELECT %s%s%s%s',
206 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
211 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset];
217 $self->_parse_rs_attrs ($rs_attrs),
224 SELECT *, ROWNUM rownum__index FROM (
226 ) WHERE ROWNUM <= ($limit+$offset)
227 ) WHERE rownum__index >= ($offset+1)
229 Supported by B<Oracle>.
233 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
235 # mangle the input sql as we will be replacing the selector
236 $sql =~ s/^ \s* SELECT \s+ .+? \s+ (?= \b FROM \b )//ix
237 or $self->throw_exception("Unrecognizable SELECT: $sql");
239 my ($insel, $outsel) = $self->_subqueried_limit_attrs ($rs_attrs);
241 my $qalias = $self->_quote ($rs_attrs->{alias});
242 my $idx_name = $self->_quote ('rownum__index');
243 my $order_group_having = $self->_parse_rs_attrs($rs_attrs);
247 push @{$self->{limit_bind}}, [ $self->__total_bindtype => $offset + $rows ], [ $self->__offset_bindtype => $offset + 1 ];
249 SELECT $outsel FROM (
250 SELECT $outsel, ROWNUM $idx_name FROM (
251 SELECT $insel ${sql}${order_group_having}
252 ) $qalias WHERE ROWNUM <= ?
253 ) $qalias WHERE $idx_name >= ?
257 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
259 SELECT $outsel FROM (
260 SELECT $insel ${sql}${order_group_having}
261 ) $qalias WHERE ROWNUM <= ?
268 # used by _Top and _FetchFirst
269 sub _prep_for_skimming_limit {
270 my ( $self, $sql, $rs_attrs ) = @_;
272 # mangle the input sql as we will be replacing the selector
273 $sql =~ s/^ \s* SELECT \s+ .+? \s+ (?= \b FROM \b )//ix
274 or $self->throw_exception("Unrecognizable SELECT: $sql");
276 my %r = ( inner_sql => $sql );
279 my ($alias_map, $extra_order_sel);
280 ($r{in_sel}, $r{out_sel}, $alias_map, $extra_order_sel)
281 = $self->_subqueried_limit_attrs ($rs_attrs);
283 my $requested_order = delete $rs_attrs->{order_by};
284 $r{order_by_requested} = $self->_order_by ($requested_order);
286 # make up an order unless supplied
287 my $inner_order = ($r{order_by_requested}
290 { "$rs_attrs->{alias}.$_" }
291 ( $rs_attrs->{_rsroot_rsrc}->_pri_cols )
295 # localise as we already have all the bind values we need
297 local $self->{order_bind};
298 $r{order_by_inner} = $self->_order_by ($inner_order);
301 for my $ch ($self->_order_by_chunks ($inner_order)) {
302 $ch = $ch->[0] if ref $ch eq 'ARRAY';
304 $ch =~ s/\s+ ( ASC|DESC ) \s* $//ix;
305 my $dir = uc ($1||'ASC');
307 push @out_chunks, \join (' ', $ch, $dir eq 'ASC' ? 'DESC' : 'ASC' );
310 $r{order_by_reversed} = $self->_order_by (\@out_chunks);
313 # this is the order supplement magic
314 $r{mid_sel} = $r{out_sel};
315 if ($extra_order_sel) {
316 for my $extra_col (sort
317 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
318 keys %$extra_order_sel
320 $r{in_sel} .= sprintf (', %s AS %s',
322 $extra_order_sel->{$extra_col},
325 $r{mid_sel} .= ', ' . $extra_order_sel->{$extra_col};
328 # since whatever order bindvals there are, they will be realiased
329 # and need to show up in front of the entire initial inner subquery
330 # *unshift* the selector bind stack to make this happen (horrible,
331 # horrible, but we don't have another mechanism yet)
332 unshift @{$self->{select_bind}}, @{$self->{order_bind}};
335 # and this is order re-alias magic
336 for my $map ($extra_order_sel, $alias_map) {
337 for my $col (keys %$map) {
338 my $re_col = quotemeta ($col);
339 $_ =~ s/$re_col/$map->{$col}/
340 for ($r{order_by_reversed}, $r{order_by_requested});
344 # generate the rest of the sql
345 $r{grpby_having} = $self->_parse_rs_attrs ($rs_attrs);
347 $r{quoted_rs_alias} = $self->_quote ($rs_attrs->{alias});
356 SELECT TOP $limit FROM (
357 SELECT TOP $limit FROM (
358 SELECT TOP ($limit+$offset) ...
359 ) ORDER BY $reversed_original_order
360 ) ORDER BY $original_order
362 Unreliable Top-based implementation, supported by B<< MSSQL < 2005 >>.
366 Due to its implementation, this limit dialect returns B<incorrect results>
367 when $limit+$offset > total amount of rows in the resultset.
372 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
374 my %l = %{ $self->_prep_for_skimming_limit($sql, $rs_attrs) };
376 $sql = sprintf ('SELECT TOP %u %s %s %s %s',
377 $rows + ($offset||0),
384 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
389 $l{order_by_reversed},
392 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
397 $l{order_by_requested},
398 ) if ( ($offset && $l{order_by_requested}) || ($l{mid_sel} ne $l{out_sel}) );
410 ) ORDER BY $reversed_original_order
411 FETCH FIRST $limit ROWS ONLY
412 ) ORDER BY $original_order
413 FETCH FIRST $limit ROWS ONLY
416 Unreliable FetchFirst-based implementation, supported by B<< IBM DB2 <= V5R3 >>.
420 Due to its implementation, this limit dialect returns B<incorrect results>
421 when $limit+$offset > total amount of rows in the resultset.
426 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
428 my %l = %{ $self->_prep_for_skimming_limit($sql, $rs_attrs) };
430 $sql = sprintf ('SELECT %s %s %s %s FETCH FIRST %u ROWS ONLY',
435 $rows + ($offset||0),
438 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
442 $l{order_by_reversed},
446 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
450 $l{order_by_requested},
452 ) if ( ($offset && $l{order_by_requested}) || ($l{mid_sel} ne $l{out_sel}) );
457 =head2 RowCountOrGenericSubQ
459 This is not exactly a limit dialect, but more of a proxy for B<Sybase ASE>.
460 If no $offset is supplied the limit is simply performed as:
466 Otherwise we fall back to L</GenericSubQ>
470 sub _RowCountOrGenericSubQ {
472 my ($sql, $rs_attrs, $rows, $offset) = @_;
474 return $self->_GenericSubQ(@_) if $offset;
476 return sprintf <<"EOF", $rows, $sql;
489 SELECT COUNT(*) FROM $original_table cnt WHERE cnt.id < $original_table.id
490 ) BETWEEN $offset AND ($offset+$rows-1)
492 This is the most evil limit "dialect" (more of a hack) for I<really> stupid
493 databases. It works by ordering the set by some unique column, and calculating
494 the amount of rows that have a less-er value (thus emulating a L</RowNum>-like
495 index). Of course this implies the set can only be ordered by a single unique
496 column. Also note that this technique can be and often is B<excruciatingly
499 Currently used by B<Sybase ASE>, due to lack of any other option.
503 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
505 my $root_rsrc = $rs_attrs->{_rsroot_rsrc};
506 my $root_tbl_name = $root_rsrc->name;
508 # mangle the input sql as we will be replacing the selector
509 $sql =~ s/^ \s* SELECT \s+ .+? \s+ (?= \b FROM \b )//ix
510 or $self->throw_exception("Unrecognizable SELECT: $sql");
512 my ($order_by, @rest) = do {
513 local $self->{quote_char};
514 $self->_order_by_chunks ($rs_attrs->{order_by})
524 ( ref $order_by eq 'ARRAY' and @$order_by == 1 )
527 $self->throw_exception (
528 'Generic Subquery Limit does not work on resultsets without an order, or resultsets '
529 . 'with complex order criteria (multicolumn and/or functions). Provide a single, '
530 . 'unique-column order criteria.'
534 ($order_by) = @$order_by if ref $order_by;
536 $order_by =~ s/\s+ ( ASC|DESC ) \s* $//ix;
537 my $direction = lc ($1 || 'asc');
539 my ($unq_sort_col) = $order_by =~ /(?:^|\.)([^\.]+)$/;
541 my $inf = $root_rsrc->storage->_resolve_column_info (
542 $rs_attrs->{from}, [$order_by, $unq_sort_col]
545 my $ord_colinfo = $inf->{$order_by} || $self->throw_exception("Unable to determine source of order-criteria '$order_by'");
547 if ($ord_colinfo->{-result_source}->name ne $root_tbl_name) {
548 $self->throw_exception(sprintf
549 "Generic Subquery Limit order criteria can be only based on the root-source '%s'"
550 . " (aliased as '%s')", $root_rsrc->source_name, $rs_attrs->{alias},
554 # make sure order column is qualified
555 $order_by = "$rs_attrs->{alias}.$order_by"
556 unless $order_by =~ /^$rs_attrs->{alias}\./;
559 my $ucs = { $root_rsrc->unique_constraints };
560 for (values %$ucs ) {
561 if (@$_ == 1 && "$rs_attrs->{alias}.$_->[0]" eq $order_by) {
566 $self->throw_exception(
567 "Generic Subquery Limit order criteria column '$order_by' must be unique (no unique constraint found)"
570 my ($in_sel, $out_sel, $alias_map, $extra_order_sel)
571 = $self->_subqueried_limit_attrs ($rs_attrs);
573 my $cmp_op = $direction eq 'desc' ? '>' : '<';
574 my $count_tbl_alias = 'rownum__emulation';
576 my $order_sql = $self->_order_by (delete $rs_attrs->{order_by});
577 my $group_having_sql = $self->_parse_rs_attrs($rs_attrs);
579 # add the order supplement (if any) as this is what will be used for the outer WHERE
580 $in_sel .= ", $_" for keys %{$extra_order_sel||{}};
582 $sql = sprintf (<<EOS,
585 SELECT $in_sel ${sql}${group_having_sql}
587 WHERE ( SELECT COUNT(*) FROM %s %s WHERE %s $cmp_op %s ) %s
590 ( map { $self->_quote ($_) } (
594 "$count_tbl_alias.$unq_sort_col",
599 push @{$self->{limit_bind}},
600 [ $self->__offset_bindtype => $offset ], [ $self->__total_bindtype => $offset + $rows - 1];
604 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
614 # !!! THIS IS ALSO HORRIFIC !!! /me ashamed
616 # Generates inner/outer select lists for various limit dialects
617 # which result in one or more subqueries (e.g. RNO, Top, RowNum)
618 # Any non-root-table columns need to have their table qualifier
619 # turned into a column alias (otherwise names in subqueries clash
620 # and/or lose their source table)
622 # Returns inner/outer strings of SQL QUOTED selectors with aliases
623 # (to be used in whatever select statement), and an alias index hashref
624 # of QUOTED SEL => QUOTED ALIAS pairs (to maybe be used for string-subst
626 # If an order_by is supplied, the inner select needs to bring out columns
627 # used in implicit (non-selected) orders, and the order condition itself
628 # needs to be realiased to the proper names in the outer query. Thus we
629 # also return a hashref (order doesn't matter) of QUOTED EXTRA-SEL =>
630 # QUOTED ALIAS pairs, which is a list of extra selectors that do *not*
631 # exist in the original select list
632 sub _subqueried_limit_attrs {
633 my ($self, $rs_attrs) = @_;
635 $self->throw_exception(
636 'Limit dialect implementation usable only in the context of DBIC (missing $rs_attrs)'
637 ) unless ref ($rs_attrs) eq 'HASH';
639 my ($re_sep, $re_alias) = map { quotemeta $_ } ( $self->{name_sep}, $rs_attrs->{alias} );
641 # correlate select and as, build selection index
642 my (@sel, $in_sel_index);
643 for my $i (0 .. $#{$rs_attrs->{select}}) {
645 my $s = $rs_attrs->{select}[$i];
646 my $sql_sel = $self->_recurse_fields ($s);
647 my $sql_alias = (ref $s) eq 'HASH' ? $s->{-as} : undef;
651 unquoted_sql => do { local $self->{quote_char}; $self->_recurse_fields ($s) },
657 $self->throw_exception("Select argument $i ($s) without corresponding 'as'")
661 $in_sel_index->{$sql_sel}++;
662 $in_sel_index->{$self->_quote ($sql_alias)}++ if $sql_alias;
664 # record unqualified versions too, so we do not have
665 # to reselect the same column twice (in qualified and
667 if (! ref $s && $sql_sel =~ / $re_sep (.+) $/x) {
668 $in_sel_index->{$1}++;
673 # re-alias and remove any name separators from aliases,
674 # unless we are dealing with the current source alias
675 # (which will transcend the subqueries as it is necessary
676 # for possible further chaining)
677 my (@in_sel, @out_sel, %renamed);
678 for my $node (@sel) {
680 $node->{as} =~ / (?<! ^ $re_alias ) \. /x
682 $node->{unquoted_sql} =~ / (?<! ^ $re_alias ) $re_sep /x
684 $node->{as} = $self->_unqualify_colname($node->{as});
685 my $quoted_as = $self->_quote($node->{as});
686 push @in_sel, sprintf '%s AS %s', $node->{sql}, $quoted_as;
687 push @out_sel, $quoted_as;
688 $renamed{$node->{sql}} = $quoted_as;
691 push @in_sel, $node->{sql};
692 push @out_sel, $self->_quote ($node->{as});
696 # see if the order gives us anything
698 for my $chunk ($self->_order_by_chunks ($rs_attrs->{order_by})) {
700 $chunk = $chunk->[0] if (ref $chunk) eq 'ARRAY';
701 $chunk =~ s/\s+ (?: ASC|DESC ) \s* $//ix;
703 next if $in_sel_index->{$chunk};
705 $extra_order_sel{$chunk} ||= $self->_quote (
706 'ORDER__BY__' . scalar keys %extra_order_sel
711 (map { join (', ', @$_ ) } (
716 keys %extra_order_sel ? \%extra_order_sel : (),
720 sub _unqualify_colname {
721 my ($self, $fqcn) = @_;
722 $fqcn =~ s/ \. /__/xg;
730 See L<DBIx::Class/CONTRIBUTORS>.
734 You may distribute this code under the same terms as Perl itself.