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, $offset ) = @_;
98 # get selectors, and scan the order_by (if any)
99 my ($stripped_sql, $in_sel, $out_sel, $alias_map, $extra_order_sel)
100 = $self->_subqueried_limit_attrs ( $sql, $rs_attrs );
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);
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
113 $in_sel .= sprintf (', %s AS %s',
115 $extra_order_sel->{$extra_col},
118 $mid_sel .= ', ' . $extra_order_sel->{$extra_col};
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}/;
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);
133 my $qalias = $self->_quote ($rs_attrs->{alias});
134 my $idx_name = $self->_quote ('rno__row__index');
136 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1], [ $self->__total_bindtype => $offset + $rows ];
140 SELECT $out_sel FROM (
141 SELECT $mid_sel, ROW_NUMBER() OVER( $rno_ord ) AS $idx_name FROM (
142 SELECT $in_sel ${stripped_sql}${group_having}
144 ) $qalias WHERE $idx_name >= ? AND $idx_name <= ?
150 # some databases are happy with OVER (), some need OVER (ORDER BY (SELECT (1)) )
151 sub _rno_default_order {
157 SELECT SKIP $offset FIRST $limit * FROM ...
159 Suported by B<Informix>, almost like LimitOffset. According to
160 L<SQL::Abstract::Limit> C<... SKIP $offset LIMIT $limit ...> is also supported.
164 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
166 $sql =~ s/^ \s* SELECT \s+ //ix
167 or $self->throw_exception("Unrecognizable SELECT: $sql");
169 return sprintf ('SELECT %s%s%s%s',
172 push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset];
178 push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ];
182 $self->_parse_rs_attrs ($rs_attrs),
188 SELECT FIRST $limit SKIP $offset * FROM ...
190 Supported by B<Firebird/Interbase>, reverse of SkipFirst. According to
191 L<SQL::Abstract::Limit> C<... ROWS $limit TO $offset ...> is also supported.
195 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
197 $sql =~ s/^ \s* SELECT \s+ //ix
198 or $self->throw_exception("Unrecognizable SELECT: $sql");
200 return sprintf ('SELECT %s%s%s%s',
202 push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ];
207 push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset];
213 $self->_parse_rs_attrs ($rs_attrs),
220 Depending on the resultset attributes one of:
223 SELECT *, ROWNUM rownum__index FROM (
225 ) WHERE ROWNUM <= ($limit+$offset)
226 ) WHERE rownum__index >= ($offset+1)
231 SELECT *, ROWNUM rownum__index FROM (
234 ) WHERE rownum__index BETWEEN ($offset+1) AND ($limit+$offset)
240 ) WHERE ROWNUM <= ($limit+1)
242 Supported by B<Oracle>.
246 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
248 my ($stripped_sql, $insel, $outsel) = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
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);
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
262 # FIXME - this is quite expensive, and does not perform caching of any sort
263 # as soon as some of the DQ work becomes viable consider switching this
266 $rs_attrs->{order_by}
268 $rs_attrs->{_rsroot_rsrc}->storage->_order_by_is_stable(
269 $rs_attrs->{from}, $rs_attrs->{order_by}
272 # if offset is 0 (first page) the we can skip a subquery
274 push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
277 SELECT $outsel FROM (
278 SELECT $insel ${stripped_sql}${order_group_having}
279 ) $qalias WHERE ROWNUM <= ?
283 push @{$self->{limit_bind}}, [ $self->__total_bindtype => $offset + $rows ], [ $self->__offset_bindtype => $offset + 1 ];
286 SELECT $outsel FROM (
287 SELECT $outsel, ROWNUM $idx_name FROM (
288 SELECT $insel ${stripped_sql}${order_group_having}
289 ) $qalias WHERE ROWNUM <= ?
290 ) $qalias WHERE $idx_name >= ?
295 push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1 ], [ $self->__total_bindtype => $offset + $rows ];
298 SELECT $outsel FROM (
299 SELECT $outsel, ROWNUM $idx_name FROM (
300 SELECT $insel ${stripped_sql}${order_group_having}
302 ) $qalias WHERE $idx_name BETWEEN ? AND ?
307 # used by _Top and _FetchFirst below
308 sub _prep_for_skimming_limit {
309 my ( $self, $sql, $rs_attrs ) = @_;
312 my (%r, $alias_map, $extra_order_sel);
313 ($r{inner_sql}, $r{in_sel}, $r{out_sel}, $alias_map, $extra_order_sel)
314 = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
316 my $requested_order = delete $rs_attrs->{order_by};
317 $r{order_by_requested} = $self->_order_by ($requested_order);
319 # make up an order unless supplied
320 my $inner_order = ($r{order_by_requested}
323 { "$rs_attrs->{alias}.$_" }
324 ( $rs_attrs->{_rsroot_rsrc}->_pri_cols )
328 # localise as we already have all the bind values we need
330 local $self->{order_bind};
331 $r{order_by_inner} = $self->_order_by ($inner_order);
334 for my $ch ($self->_order_by_chunks ($inner_order)) {
335 $ch = $ch->[0] if ref $ch eq 'ARRAY';
337 $ch =~ s/\s+ ( ASC|DESC ) \s* $//ix;
338 my $dir = uc ($1||'ASC');
340 push @out_chunks, \join (' ', $ch, $dir eq 'ASC' ? 'DESC' : 'ASC' );
343 $r{order_by_reversed} = $self->_order_by (\@out_chunks);
346 # this is the order supplement magic
347 $r{mid_sel} = $r{out_sel};
348 if ($extra_order_sel) {
349 for my $extra_col (sort
350 { $extra_order_sel->{$a} cmp $extra_order_sel->{$b} }
351 keys %$extra_order_sel
353 $r{in_sel} .= sprintf (', %s AS %s',
355 $extra_order_sel->{$extra_col},
358 $r{mid_sel} .= ', ' . $extra_order_sel->{$extra_col};
361 # Whatever order bindvals there are, they will be realiased and
362 # need to show up in front of the entire initial inner subquery
363 push @{$self->{pre_select_bind}}, @{$self->{order_bind}};
366 # and this is order re-alias magic
367 for my $map ($extra_order_sel, $alias_map) {
368 for my $col (keys %$map) {
369 my $re_col = quotemeta ($col);
370 $_ =~ s/$re_col/$map->{$col}/
371 for ($r{order_by_reversed}, $r{order_by_requested});
375 # generate the rest of the sql
376 $r{grpby_having} = $self->_parse_rs_attrs ($rs_attrs);
378 $r{quoted_rs_alias} = $self->_quote ($rs_attrs->{alias});
387 SELECT TOP $limit FROM (
388 SELECT TOP $limit FROM (
389 SELECT TOP ($limit+$offset) ...
390 ) ORDER BY $reversed_original_order
391 ) ORDER BY $original_order
393 Unreliable Top-based implementation, supported by B<< MSSQL < 2005 >>.
397 Due to its implementation, this limit dialect returns B<incorrect results>
398 when $limit+$offset > total amount of rows in the resultset.
403 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
405 my %l = %{ $self->_prep_for_skimming_limit($sql, $rs_attrs) };
407 $sql = sprintf ('SELECT TOP %u %s %s %s %s',
408 $rows + ($offset||0),
415 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
420 $l{order_by_reversed},
423 $sql = sprintf ('SELECT TOP %u %s FROM ( %s ) %s %s',
428 $l{order_by_requested},
429 ) if ( ($offset && $l{order_by_requested}) || ($l{mid_sel} ne $l{out_sel}) );
441 ) ORDER BY $reversed_original_order
442 FETCH FIRST $limit ROWS ONLY
443 ) ORDER BY $original_order
444 FETCH FIRST $limit ROWS ONLY
447 Unreliable FetchFirst-based implementation, supported by B<< IBM DB2 <= V5R3 >>.
451 Due to its implementation, this limit dialect returns B<incorrect results>
452 when $limit+$offset > total amount of rows in the resultset.
457 my ( $self, $sql, $rs_attrs, $rows, $offset ) = @_;
459 my %l = %{ $self->_prep_for_skimming_limit($sql, $rs_attrs) };
461 $sql = sprintf ('SELECT %s %s %s %s FETCH FIRST %u ROWS ONLY',
466 $rows + ($offset||0),
469 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
473 $l{order_by_reversed},
477 $sql = sprintf ('SELECT %s FROM ( %s ) %s %s FETCH FIRST %u ROWS ONLY',
481 $l{order_by_requested},
483 ) if ( ($offset && $l{order_by_requested}) || ($l{mid_sel} ne $l{out_sel}) );
488 =head2 RowCountOrGenericSubQ
490 This is not exactly a limit dialect, but more of a proxy for B<Sybase ASE>.
491 If no $offset is supplied the limit is simply performed as:
497 Otherwise we fall back to L</GenericSubQ>
501 sub _RowCountOrGenericSubQ {
503 my ($sql, $rs_attrs, $rows, $offset) = @_;
505 return $self->_GenericSubQ(@_) if $offset;
507 return sprintf <<"EOF", $rows, $sql;
520 SELECT COUNT(*) FROM $original_table cnt WHERE cnt.id < $original_table.id
521 ) BETWEEN $offset AND ($offset+$rows-1)
523 This is the most evil limit "dialect" (more of a hack) for I<really> stupid
524 databases. It works by ordering the set by some unique column, and calculating
525 the amount of rows that have a less-er value (thus emulating a L</RowNum>-like
526 index). Of course this implies the set can only be ordered by a single unique
527 column. Also note that this technique can be and often is B<excruciatingly
530 Currently used by B<Sybase ASE>, due to lack of any other option.
534 my ($self, $sql, $rs_attrs, $rows, $offset) = @_;
536 my $root_rsrc = $rs_attrs->{_rsroot_rsrc};
537 my $root_tbl_name = $root_rsrc->name;
539 my ($order_by, @rest) = do {
540 local $self->{quote_char};
541 $self->_order_by_chunks ($rs_attrs->{order_by})
551 ( ref $order_by eq 'ARRAY' and @$order_by == 1 )
554 $self->throw_exception (
555 'Generic Subquery Limit does not work on resultsets without an order, or resultsets '
556 . 'with complex order criteria (multicolumn and/or functions). Provide a single, '
557 . 'unique-column order criteria.'
561 ($order_by) = @$order_by if ref $order_by;
563 $order_by =~ s/\s+ ( ASC|DESC ) \s* $//ix;
564 my $direction = lc ($1 || 'asc');
566 my ($unq_sort_col) = $order_by =~ /(?:^|\.)([^\.]+)$/;
568 my $inf = $root_rsrc->storage->_resolve_column_info (
569 $rs_attrs->{from}, [$order_by, $unq_sort_col]
572 my $ord_colinfo = $inf->{$order_by} || $self->throw_exception("Unable to determine source of order-criteria '$order_by'");
574 if ($ord_colinfo->{-result_source}->name ne $root_tbl_name) {
575 $self->throw_exception(sprintf
576 "Generic Subquery Limit order criteria can be only based on the root-source '%s'"
577 . " (aliased as '%s')", $root_rsrc->source_name, $rs_attrs->{alias},
581 # make sure order column is qualified
582 $order_by = "$rs_attrs->{alias}.$order_by"
583 unless $order_by =~ /^$rs_attrs->{alias}\./;
586 my $ucs = { $root_rsrc->unique_constraints };
587 for (values %$ucs ) {
588 if (@$_ == 1 && "$rs_attrs->{alias}.$_->[0]" eq $order_by) {
593 $self->throw_exception(
594 "Generic Subquery Limit order criteria column '$order_by' must be unique (no unique constraint found)"
597 my ($stripped_sql, $in_sel, $out_sel, $alias_map, $extra_order_sel)
598 = $self->_subqueried_limit_attrs ($sql, $rs_attrs);
600 my $cmp_op = $direction eq 'desc' ? '>' : '<';
601 my $count_tbl_alias = 'rownum__emulation';
603 my $order_sql = $self->_order_by (delete $rs_attrs->{order_by});
604 my $group_having_sql = $self->_parse_rs_attrs($rs_attrs);
606 # add the order supplement (if any) as this is what will be used for the outer WHERE
607 $in_sel .= ", $_" for keys %{$extra_order_sel||{}};
611 $rownum_cond = 'BETWEEN ? AND ?';
613 push @{$self->{limit_bind}},
614 [ $self->__offset_bindtype => $offset ],
615 [ $self->__total_bindtype => $offset + $rows - 1]
619 $rownum_cond = '< ?';
621 push @{$self->{limit_bind}},
622 [ $self->__rows_bindtype => $rows ]
629 SELECT $in_sel ${stripped_sql}${group_having_sql}
631 WHERE ( SELECT COUNT(*) FROM %s %s WHERE %s $cmp_op %s ) $rownum_cond
633 ", map { $self->_quote ($_) } (
637 "$count_tbl_alias.$unq_sort_col",
643 # !!! THIS IS ALSO HORRIFIC !!! /me ashamed
645 # Generates inner/outer select lists for various limit dialects
646 # which result in one or more subqueries (e.g. RNO, Top, RowNum)
647 # Any non-root-table columns need to have their table qualifier
648 # turned into a column alias (otherwise names in subqueries clash
649 # and/or lose their source table)
651 # Returns mangled proto-sql, inner/outer strings of SQL QUOTED selectors
652 # with aliases (to be used in whatever select statement), and an alias
653 # index hashref of QUOTED SEL => QUOTED ALIAS pairs (to maybe be used
654 # for string-subst higher up).
655 # If an order_by is supplied, the inner select needs to bring out columns
656 # used in implicit (non-selected) orders, and the order condition itself
657 # needs to be realiased to the proper names in the outer query. Thus we
658 # also return a hashref (order doesn't matter) of QUOTED EXTRA-SEL =>
659 # QUOTED ALIAS pairs, which is a list of extra selectors that do *not*
660 # exist in the original select list
661 sub _subqueried_limit_attrs {
662 my ($self, $proto_sql, $rs_attrs) = @_;
664 $self->throw_exception(
665 'Limit dialect implementation usable only in the context of DBIC (missing $rs_attrs)'
666 ) unless ref ($rs_attrs) eq 'HASH';
668 # mangle the input sql as we will be replacing the selector entirely
670 $rs_attrs->{_selector_sql}
672 $proto_sql =~ s/^ \s* SELECT \s* \Q$rs_attrs->{_selector_sql}//ix
674 $self->throw_exception("Unrecognizable SELECT: $proto_sql");
677 my ($re_sep, $re_alias) = map { quotemeta $_ } ( $self->{name_sep}, $rs_attrs->{alias} );
679 # insulate from the multiple _recurse_fields calls below
680 local $self->{select_bind};
682 # correlate select and as, build selection index
683 my (@sel, $in_sel_index);
684 for my $i (0 .. $#{$rs_attrs->{select}}) {
686 my $s = $rs_attrs->{select}[$i];
687 my $sql_sel = $self->_recurse_fields ($s);
688 my $sql_alias = (ref $s) eq 'HASH' ? $s->{-as} : undef;
693 local $self->{quote_char};
694 $self->_recurse_fields ($s);
701 $self->throw_exception("Select argument $i ($s) without corresponding 'as'")
705 $in_sel_index->{$sql_sel}++;
706 $in_sel_index->{$self->_quote ($sql_alias)}++ if $sql_alias;
708 # record unqualified versions too, so we do not have
709 # to reselect the same column twice (in qualified and
711 if (! ref $s && $sql_sel =~ / $re_sep (.+) $/x) {
712 $in_sel_index->{$1}++;
717 # re-alias and remove any name separators from aliases,
718 # unless we are dealing with the current source alias
719 # (which will transcend the subqueries as it is necessary
720 # for possible further chaining)
721 my (@in_sel, @out_sel, %renamed);
722 for my $node (@sel) {
724 $node->{as} =~ / (?<! ^ $re_alias ) \. /x
726 $node->{unquoted_sql} =~ / (?<! ^ $re_alias ) $re_sep /x
728 $node->{as} = $self->_unqualify_colname($node->{as});
729 my $quoted_as = $self->_quote($node->{as});
730 push @in_sel, sprintf '%s AS %s', $node->{sql}, $quoted_as;
731 push @out_sel, $quoted_as;
732 $renamed{$node->{sql}} = $quoted_as;
735 push @in_sel, $node->{sql};
736 push @out_sel, $self->_quote ($node->{as});
739 # see if the order gives us anything
741 for my $chunk ($self->_order_by_chunks ($rs_attrs->{order_by})) {
743 $chunk = $chunk->[0] if (ref $chunk) eq 'ARRAY';
744 $chunk =~ s/\s+ (?: ASC|DESC ) \s* $//ix;
746 next if $in_sel_index->{$chunk};
748 $extra_order_sel{$chunk} ||= $self->_quote (
749 'ORDER__BY__' . scalar keys %extra_order_sel
755 (map { join (', ', @$_ ) } (
760 keys %extra_order_sel ? \%extra_order_sel : (),
764 sub _unqualify_colname {
765 my ($self, $fqcn) = @_;
766 $fqcn =~ s/ \. /__/xg;
774 See L<DBIx::Class/CONTRIBUTORS>.
778 You may distribute this code under the same terms as Perl itself.