此触发器应从父表中删除未从子表中删除的行。错误如下图所示。
我的代码尝试:
CREATE TRIGGER ProductDeleted ON Product
for DELETE AS
BEGIN
DELETE FROM OrderItem
WHERE ProductID = (SELECT ProductID FROM DELETED)
END
请帮助我
答案 0 :(得分:2)
您可以通过在外键约束(例如
)上添加CASCADE DELETE提示来简化它 CREATE TABLE OrderItem
(
ID INT ,
ProductID NOT NULL UNIQUE
CONSTRAINT fk_Products
REFERENCES Products (ID) ON DELETE CASCADE
);
由于您已有表,因此您只需删除约束并重新创建一个新表。
ALTER TABLE OrderItem DROP
CONSTRAINT fk_ProductID;
ALTER TABLE OrderItem ADD
CONSTRAINT fk_ProductID
FOREIGN KEY (ID)
REFERENCES Product (ID)
ON DELETE CASCADE;
这意味着,无论何时从父表(Product)中删除记录,来自(OrderItem)的子记录也将被删除,因此您不必使用触发器,除非您想要这样做一些录音。
如果你真的坚持使用触发器,那么你可以稍微调整它:
ALTER TRIGGER ProductDeleted on Product
INSTEAD OF DELETE AS
BEGIN
SET NOCOUNT ON;
/* First we are deleting referenced columns in OrderItem table */
DELETE FROM OrderItem
where ProductID IN (select deleted.ID /* Columns from product Table */ from deleted)
/* Now we are doing actual delete statement */
DELETE FROM Products where ID IN (select deleted.ID from deleted)
END
但是再一次你应该考虑使用ON CASCADE DELETE,它更容易设置,更容易维护,每个表只能有一个INSTEAD OF触发器,所以如果你需要做一些更有意义的事情你就必须改变这个,并增加额外的开销。
答案 1 :(得分:0)
添加SET NOCOUNT ON
作为触发器正文中的第一件事(BEGIN
之后)。