MySQL触发器的使用场景及方法实例

CREATE TRIGGER newproduct AFTER INSERT on products FOR EACH ROW
BEGIN
 DECLARE msg VARCHAR(100);
 SET msg = "products added";
 SIGNAL SQLSTATE 'HY000' SET message_text = msg;
 
END

#newproduct 触发器的名字
CREATE TRIGGER newproduct

DECLARE msg VARCHAR(100);

SIGNAL SQLSTATE 'HY000' SET message_text = msg;

-- 删除触发器
DROP TRIGGER newproduct;

CREATE TRIGGER neworder AFTER INSERT ON orders for EACH ROW
 SELECT NEW.order_num into @ee;

insert INTO orders(order_date,cust_id) VALUES(NOW(),10001);
SELECT @ee as num;

drop TRIGGER neworder;

SELECT NEW.order_num into @a;

insert INTO orders(order_date,cust_id) VALUES(NOW(),10001);
SELECT @ee as num;

drop TRIGGER neworder;

CREATE TRIGGER trg_course_in 
BEFORE INSERT ON course
FOR EACH ROW
BEGIN
  DECLARE msg VARCHAR(100); 
  IF EXISTS (SELECT * FROM course where cname=NEW.cname) THEN 
   SET msg='不能输入相同名称的课程'; 
   SIGNAL SQLSTATE 'HY000' SET message_text = msg; 
  END IF; 
 
END

CREATE TRIGGER trg_ssex AFTER INSERT on student FOR EACH ROW
BEGIN
 DECLARE msg VARCHAR(100);
 IF(NEW.ssex not in('男','女')) THEN
 SET msg ='性别必须为男或女'; 
 SIGNAL SQLSTATE 'HY000' SET message_text = msg;
 END IF
END

CREATE TRIGGER UPDATEevendor BEFORE UPDATE on vendors
FOR EACH ROW SET new.vend_state =UPPER(new.vend_state);

UPDATE vendors SET vend_state='hw' where vend_id='1001';
DROP TRIGGER UPDATEevendor;

CREATE TRIGGER trg_student_updateSno BEFORE UPDATE
FOR EACH ROW
BEGIN
 DECLARE msg VARCHAR(100); 
 IF NEW.sno <> OLD.sno THEN 
 SET msg='不允许修改sno'; 
 SIGNAL SQLSTATE 'HY000' SET message_text = msg; 
 END IF; 
END

CREATE TABLE archive_orders LIKE orders;

-- 创建一个删除的触发器
CREATE TRIGGER deleteorder BEFORE DELETE on orders
for EACH ROW BEGIN
INSERT INTO archive_orders(order_num,order_date,cust_id) VALUES(old.order_num,old.order_date,old.cust_id);
END

DELETE FROM orders WHERE order_num='20014';

SELECT * FROM archive_orders;