MySQL BEFORE UPDATE触发器 - 更改值

Question

所以,我有一个名为employees的MySQL表.

ID    name    meta
0     jack    ok
1     anne    del

我想写一个触发器来阻止meta ='del'的行来更新元字段.所以,如果我这样做:

UPDATE employees SET meta = 'busy' WHERE ID = 0

该行应该更新,元将"忙"

但当我这样做时:

UPDATE employees SET meta = 'busy' WHERE ID = 1

元字段应该仍然是'del'

我试过了:

delimiter $$
CREATE TRIGGER updateEmployees
BEFORE UPDATE ON employees
FOR EACH ROW 
BEGIN
    IF OLD.meta = 'del' THEN
        NEW.meta = 'del'
    END IF;
END$$
delimiter ;

但MySQL返回时出现语法错误.有任何想法吗？

Answer 1

你忘了添加SET子句.这样它实际上不会改变值.

delimiter $$
CREATE TRIGGER updateEmployees
BEFORE UPDATE ON employees
FOR EACH ROW 
BEGIN
    IF OLD.meta = 'del' THEN
        SET NEW.meta = 'del';
    END IF;
END$$
delimiter ;

Answer 2

你错过了;

delimiter $$
CREATE TRIGGER updateEmployees
BEFORE UPDATE ON employees
FOR EACH ROW 
BEGIN
    IF OLD.meta = 'del' THEN
        NEW.meta = 'del';   -- << here
    END IF;
END$$
delimiter ;

触发是邪恶的。

触发的替代方法是添加另一个条件AND

UPDATE employees 
SET    meta = 'busy' 
WHERE  ID = 1 AND meta <> 'del'