-- -- 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;