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