DB2 and MSSQL have different default order syntaxes

[dbsrgits/DBIx-Class.git] / lib / DBIx / Class / SQLAHacks.pm

diff --git a/lib/DBIx/Class/SQLAHacks.pm b/lib/DBIx/Class/SQLAHacks.pm
index 81661fb..02c336c 100644 (file)
--- a/lib/DBIx/Class/SQLAHacks.pm
+++ b/lib/DBIx/Class/SQLAHacks.pm
@@ -47,31 +47,36 @@ sub new {
 }
 
 
-# Slow but ANSI standard Limit/Offset support. DB2 uses this
+# ANSI standard Limit/Offset implementation. DB2 and MSSQL use this
 sub _RowNumberOver {
   my ($self, $sql, $order, $rows, $offset ) = @_;
 
-  $offset += 1;
-  my $last = $rows + $offset - 1;
-  my ( $order_by ) = $self->_order_by( $order );
+  # get the order_by only (or make up an order if none exists)
+  my $order_by = $self->_order_by(
+    (delete $order->{order_by}) || $self->_rno_default_order
+  );
 
-  $sql = <<"SQL";
-SELECT * FROM
-(
-   SELECT Q1.*, ROW_NUMBER() OVER( ) AS ROW_NUM FROM (
-      $sql
-      $order_by
-   ) Q1
-) Q2
-WHERE ROW_NUM BETWEEN $offset AND $last
+  # whatever is left
+  my $group_having = $self->_order_by($order);
 
-SQL
+  $sql = sprintf (<<'EOS', $order_by, $sql, $group_having, $offset + 1, $offset + $rows, );
+
+SELECT * FROM (
+  SELECT orig_query.*, ROW_NUMBER() OVER(%s ) AS rno__row__index FROM (%s%s) orig_query
+) rno_subq WHERE rno__row__index BETWEEN %d AND %d
 
+EOS
+
+  $sql =~ s/\s*\n\s*/ /g;   # easier to read in the debugger
   return $sql;
 }
 
-# Crappy Top based Limit/Offset support. MSSQL uses this currently,
-# but may have to switch to RowNumberOver one day
+# some databases are happy with OVER (), some need OVER (ORDER BY (SELECT (1)) )
+sub _rno_default_order {
+  return undef;
+}
+
+# Crappy Top based Limit/Offset support. Legacy from MSSQL.
 sub _Top {
   my ( $self, $sql, $order, $rows, $offset ) = @_;