return sprintf ('SELECT %s%s%s%s',
$offset
? do {
- push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset];
+ push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset];
'SKIP ? '
}
: ''
,
do {
- push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
+ push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ];
'FIRST ? '
},
$sql,
return sprintf ('SELECT %s%s%s%s',
do {
- push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
+ push @{$self->{pre_select_bind}}, [ $self->__rows_bindtype => $rows ];
'FIRST ? '
},
$offset
? do {
- push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset];
+ push @{$self->{pre_select_bind}}, [ $self->__offset_bindtype => $offset];
'SKIP ? '
}
: ''
);
}
+
=head2 RowNum
+Depending on the resultset attributes one of:
+
SELECT * FROM (
SELECT *, ROWNUM rownum__index FROM (
SELECT ...
) WHERE ROWNUM <= ($limit+$offset)
) WHERE rownum__index >= ($offset+1)
+or
+
+ SELECT * FROM (
+ SELECT *, ROWNUM rownum__index FROM (
+ SELECT ...
+ )
+ ) WHERE rownum__index BETWEEN ($offset+1) AND ($limit+$offset)
+
+or
+
+ SELECT * FROM (
+ SELECT ...
+ ) WHERE ROWNUM <= ($limit+1)
+
Supported by B<Oracle>.
=cut
my $idx_name = $self->_quote ('rownum__index');
my $order_group_having = $self->_parse_rs_attrs($rs_attrs);
+ #
+ # There are two ways to limit in Oracle, one vastly faster than the other
+ # on large resultsets: https://decipherinfosys.wordpress.com/2007/08/09/paging-and-countstopkey-optimization/
+ # However Oracle is retarded and does not preserve stable ROWNUM() values
+ # when called twice in the same scope. Therefore unless the resultset is
+ # ordered by a unique set of columns, it is not safe to use the faster
+ # method, and the slower BETWEEN query is used instead
+ #
+ # FIXME - this is quite expensive, and doe snot perform caching of any sort
+ # as soon as some of the DQ work becomes viable consider switching this
+ # over
+ if ( __order_by_is_unique($rs_attrs) ) {
+
+ # if offset is 0 (first page) the we can skip a subquery
+ if (! $offset) {
+ push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
+
+ return <<EOS;
+SELECT $outsel FROM (
+ SELECT $insel ${stripped_sql}${order_group_having}
+) $qalias WHERE ROWNUM <= ?
+EOS
+ }
+ else {
+ push @{$self->{limit_bind}}, [ $self->__total_bindtype => $offset + $rows ], [ $self->__offset_bindtype => $offset + 1 ];
- if ($offset) {
-
- push @{$self->{limit_bind}}, [ $self->__total_bindtype => $offset + $rows ], [ $self->__offset_bindtype => $offset + 1 ];
-
- return <<EOS;
+ return <<EOS;
SELECT $outsel FROM (
SELECT $outsel, ROWNUM $idx_name FROM (
SELECT $insel ${stripped_sql}${order_group_having}
) $qalias WHERE ROWNUM <= ?
) $qalias WHERE $idx_name >= ?
EOS
-
+ }
}
else {
- push @{$self->{limit_bind}}, [ $self->__rows_bindtype => $rows ];
+ push @{$self->{limit_bind}}, [ $self->__offset_bindtype => $offset + 1 ], [ $self->__total_bindtype => $offset + $rows ];
return <<EOS;
- SELECT $outsel FROM (
+SELECT $outsel FROM (
+ SELECT $outsel, ROWNUM $idx_name FROM (
SELECT $insel ${stripped_sql}${order_group_having}
- ) $qalias WHERE ROWNUM <= ?
+ ) $qalias
+) $qalias WHERE $idx_name BETWEEN ? AND ?
EOS
+ }
+}
+
+# determine if the supplied order_by contains a unique column (set)
+sub __order_by_is_unique {
+ my $rs_attrs = shift;
+ my $rsrc = $rs_attrs->{_rsroot_rsrc};
+ my $order_by = $rs_attrs->{order_by}
+ || return 0;
+
+ my $storage = $rsrc->schema->storage;
+ my @order_by_cols = map { $_->[0] } $storage->_extract_order_criteria($order_by)
+ or return 0;
+
+ my $colinfo =
+ $storage->_resolve_column_info($rs_attrs->{from}, \@order_by_cols);
+
+ my $sources = {
+ map {( "$_" => $_ )} map { $_->{-result_source} } values %$colinfo
+ };
+
+ my $supplied_order = {
+ map { $_ => 1 }
+ grep { exists $colinfo->{$_} and ! $colinfo->{$_}{is_nullable} }
+ @order_by_cols
+ };
+
+ return 0 unless keys %$supplied_order;
+
+ for my $uks (
+ map { values %$_ } map { +{ $_->unique_constraints } } values %$sources
+ ) {
+ return 1
+ unless first { ! exists $supplied_order->{$_} } @$uks;
}
+
+ return 0;
}
-# used by _Top and _FetchFirst
+# used by _Top and _FetchFirst below
sub _prep_for_skimming_limit {
my ( $self, $sql, $rs_attrs ) = @_;
$r{mid_sel} .= ', ' . $extra_order_sel->{$extra_col};
}
- # since whatever order bindvals there are, they will be realiased
- # and need to show up in front of the entire initial inner subquery
- # *unshift* the selector bind stack to make this happen (horrible,
- # horrible, but we don't have another mechanism yet)
- unshift @{$self->{select_bind}}, @{$self->{order_bind}};
+ # Whatever order bindvals there are, they will be realiased and
+ # need to show up in front of the entire initial inner subquery
+ push @{$self->{pre_select_bind}}, @{$self->{order_bind}};
}
# and this is order re-alias magic
#
# Returns mangled proto-sql, inner/outer strings of SQL QUOTED selectors
# with aliases (to be used in whatever select statement), and an alias
-# index hashref of QUOTED SEL => QUOTED ALIAS pairs (to maybe be used
+# index hashref of QUOTED SEL => QUOTED ALIAS pairs (to maybe be used
# for string-subst higher up).
# If an order_by is supplied, the inner select needs to bring out columns
# used in implicit (non-selected) orders, and the order condition itself