Question

USE `DEPT`;
DELIMITER $$
CREATE DEFINER=`root`@`localhost` TRIGGER `R3` AFTER UPDATE ON `EMPLOYEE` FOR EACH ROW BEGIN
    Declare salary int;
    SET salary = (select SUM(Salary) as salary from Employee where Employee.Dno = New.Dno group by Employee.Dno);
    UPDATE DEPARTMENT set Total_sal = salary where Dno = NEW.Dno;
END

薪水是空的，并且因为不可能而抛出错误。

Answer 1

如果您收到salary为NULL的错误，则问题不在于此触发器。

这是更新后的触发器，会影响department.tot_salary的值。如果此字段出现问题，则错误会显示为tot_salary，而不是salary。

表salary会发生employee错误，并且执行此触发器之前会发生。该字段的值可能不是NULL。

我的结论是，您尝试使用NULL salary值更新员工记录，并且该字段中不允许该值。

Answer 2

错误是由于列名称与变量名salary发生冲突使用相关名称但与列名称不同的名称始终是一个好习惯。

在更新部门表中的总薪水时，您还需要进行一些逻辑更改只要添加新员工，您只需更新部门的总薪水您还应该为转移此员工的部门更改相同的内容。

更改触发后应该正常工作：

drop trigger if exists `R3`;

DELIMITER $$

CREATE TRIGGER `R3` AFTER UPDATE ON `EMPLOYEE` FOR EACH ROW BEGIN
    Declare old_dept_total_salary int;
    Declare new_dept_total_salary int;

    -- if emp is moved to a new dept, then
    -- former dept tot sal affects
    select SUM(Salary) into old_dept_total_salary 
      from Employee  
     where Employee.deptno = OLD.deptno 
     group by Employee.deptno;

    -- update it
    UPDATE DEPARTMENT 
       SET Total_sal = old_dept_total_salary
     WHERE deptno = OLD.deptno;

    -- if emp is moved to a new dept, then
    -- new dept tot sal too affects
    select SUM(Salary) into new_dept_total_salary 
      from Employee 
     where Employee.deptno = New.deptno 
     group by Employee.deptno;

    -- update it
    UPDATE DEPARTMENT 
       SET Total_sal = new_dept_total_salary
     WHERE deptno = NEW.deptno;
END;
$$

delimiter ;

每当插入新员工或旧员工时，您还需要after insert上的after delete和employee触发器来更正total_sal表的department字段员工被删除。

演示 @ MySQL 5.5.32 Fiddle

为什么这个SQL触发器不起作用？选择总和并更新

2 个答案: