mysql - 更新触发器.. 没有按预期工作？

Question

我正在学习如何在 MYSQL 中构建触发器，我构建了一个触发器，如果​​其中一名部门员工更新(更新他们的薪水或将他们添加到部门/从部门删除)，它将重新计算部门薪水。如果我更新用户的薪水，它也不会更新部门的薪水。

员工表:

SSN
Salary
Name
Dno
Supervisor_ssn

部门表:

DName
Dno
Total_sal
Manager_SSN

触发器如下所示:

DELIMITER $$
CREATE TRIGGER `Employee_AUPD` AFTER UPDATE ON `Employee` FOR EACH ROW
BEGIN
 IF old.salary != new.salary THEN
    UPDATE department SET total_sal = total_sal - old.salary
        WHERE new.dno = department.dno;
    UPDATE department SET total_sal = total_sal + new.salary
        WHERE new.dno = department.dno;
 END IF;
 IF old.dno != new.dno THEN
    UPDATE department SET total_sal = total_sal - old.salary
        WHERE old.dno = department.dno;
    UPDATE department SET total_sal = total_sal + new.salary
        WHERE new.dno = department.dno;
 END IF;
END;
DELIMITER;

Answer 1

你有一个逻辑错误。如果工资和部门发生变化，第一个 IF block 从新部门中减去旧工资。

但是您不需要测试任何东西。简单地编写这两个更新语句:

UPDATE department SET
total_sal = total_sal - old.salary
WHERE department.dno = old.dno;

UPDATE department SET
total_sal = total_sal + new.salary
WHERE department.dno = new.dno;

这个逻辑是稳健的，不会失败。