...$a_query .= "pc.product_code_id,pc.product_code_price ";
$a_query .= "* CASE WHEN ISNULL(s.special_percentage) OR s.start_date>CURDATE() OR s.end_date<CURDATE() ";
$a_query .= "THEN 1 ELSE (100-s.special_percentage)*.01 END AS price FROM product_codes pc "...