为什么这个触发器不按我想要的方式工作？

Question

我在我的mysql数据库中有两个表： 顾问：编号 学生：advisorID |主要

我想更新学生，其中Advisor中删除的ID等于advisorID并使用一组if语句来根据该学生的专业更改该学生的advisorID值。这是我迄今为止：

delimiter // 
    create trigger advisor_delete after delete 
    on advisor 
     UPDATE Student 
      IF Student.major = 'major1' THEN SET Student.advisorID = 1; 
      ELSEIF Student.major = 'major2' THEN SET Student.advisorID = 2; 
      ELSEIF Student.major = 'major3' THEN SET Student.advisorID = 3; 
      ELSE SET Student.advisorID = 4; 
      ENDIF; 
     WHERE Student.advisorID = OLD.id; 
    end// 

任何帮助是值得欢迎的。谢谢。

Answer 1

我不知道这UPDATE/IFELSEIF语法，但CASE声明会为你工作：

delimiter // 
create trigger advisor_delete after delete 
on advisor 
    UPDATE Student 
     SET Student.advisorID = 
      CASE Student.major WHEN 'major1' THEN 1 
           WHEN 'major2' THEN 2 
           WHEN 'major3' THEN 3 
           ELSE 4 
      END 
    WHERE Student.advisorID = OLD.id; 
end//