foreach $c1(@c1) {
        foreach $c2(@c2)
        {
            $sth = $dbh->prepare( "SELECT a1.id FROM a1, a1_b1, b1  WHERE b1.id = '$c1'AND a1_b1.a1_id=a1.id AND a1_b1.b1_id=b1.id );                                                       
             $sth->execute;
             my $row = $sth->fetchrow(); 
            $sth = $dbh->prepare( "SELECT a1.id  FROM a1, a1_b1, b1 WHERE b1.id = '$c2' AND a1_b1.a1_id=a1.id AND a1_b1.b1_id=b1.id );                                                                                        
             $sth->execute;                                                  
             my $row1 = $sth->fetchrow( );
            if ($row1 == $row2)
              {
              push @row, $row1;
              }