mysql

Question

我正在尝试制作一个触发器，检查更新后员工的薪水是否低于其经理的薪水，如果是，则中止更新。

CREATE TRIGGER Employee_BeforeUpdate
 BEFORE UPDATE ON Employee
  FOR EACH ROW
  BEGIN
   IF EXISTS (
     SELECT * FROM Manager, Manages
     WHERE NEW.eid = Manages.eid
     AND Manager.mid = Manages.mid
     AND NEW.salary > Manager.salary)
   THEN SIGNAL SQLSTATE '45000' SET message_text = 'Error message';
   END IF;
 END;

我在第 9 行的“”附近遇到语法错误 (1064)，我不知道为什么。这也是触发的正确方法吗？

(MySql 版本 5.7.23-0ubuntu.18.04.1)

CREATE TABLE Employee (eid char(5), salary integer, primary key(eid));
CREATE TABLE Manager (mid char(5), salary integer, primary key(mid));
CREATE TABLE Manages (mid char(5), eid char(5) , primary key (mid,eid),
                      foreign key(mid) references Manager(mid),
                      foreign key(eid) references Employee(eid));

Answer 1

您需要将 Delimiter 重新定义为其他内容（例如：$$），而不是 (;).
同时作为一项安全措施，检查是否已经存在同名触发器(DROP TRIGGER IF EXISTS)
最后，将DELIMITER重新定义为;

将触发器更改为如下：

DELIMITER $$
DROP TRIGGER IF EXISTS Employee_BeforeUpdate $$
CREATE TRIGGER Employee_BeforeUpdate
 BEFORE UPDATE ON Employee
  FOR EACH ROW
  BEGIN
   IF EXISTS (
     SELECT * FROM Manager, Manages
     WHERE NEW.eid = Manages.eid
     AND Manager.mid = Manages.mid
     AND NEW.salary > Manager.salary)
   THEN SIGNAL SQLSTATE '45000' SET message_text = 'Error message';
   END IF;
 END $$
DELIMITER ;

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