--
-- ec_one_gift_cert_on_one_order/2
--
create or replace function ec_one_gift_cert_on_one_order(
  integer,
  integer
) returns numeric as $$

DECLARE
	v_gift_certificate_id	alias for $1;
	v_order_id		alias for $2;
        bal_amount_used         numeric;
BEGIN
        select coalesce(sum(amount_used),0)-coalesce(sum(amount_reinstated),0) into bal_amount_used
        from ec_gift_certificate_usage
        where order_id=v_order_id
        and gift_certificate_id=v_gift_certificate_id;

        RETURN bal_amount_used;

END;$$ language plpgsql;