求教以下代码
create or replace trigger BillMadeUpdate
before update of made on bill
for each row
DECLARE
CURSOR curBF(billUUID bf.billuuid%type) IS SELECT BillUUID, FoodId, Copies FROM bf WHERE BillUUID = :new.billUUID;
CURSOR curFM(foodId fm.foodid%type) IS SELECT * FROM fm WHERE FoodId = foodId;
foodId bf.foodid%type; -- 菜编号
copies bf.copies%type; -- 份数
materialID fm.materialid%type; -- 食材编号
materialNum fm.materialnumber%type; -- 食材量
BEGIN
-- 一个订单会有多道菜
FOR r in curBF(:new.BillUUID)
LOOP
foodId := r.FoodId;
copies := r.copies;
-- 一道菜对应多种食材
FOR r1 IN curFM(foodId)
LOOP
materialID := r1.MaterialId;
materialNum := r1.Materialnumber * copies;
UPDATE Material SET Remain = Remain - materialNum WHERE r1.MaterialId = materialId;
END LOOP;
END LOOP;
end BillMadeUpdate;
上面运行不明白多减去了什么