mysql - 尝试触发更新时出现错误 1442

Question

我试图触发 chatroompost.view 的更新更新发生时从 1 到 0 和 chatroompost.likecount <= -5

CREATE TRIGGER `chatroompost_AFTER_UPDATE` 
AFTER UPDATE ON `chatroompost` 
FOR EACH ROW BEGIN  
    IF (NEW.likecount <= -5) THEN
        UPDATE `chatroompost` SET NEW.`view`='0'  WHERE `chatroompost`.`idchatroompost` = OLD.`idchatroompost`;   
    END IF;  
END $$ 
DELIMITER ;

查询:

UPDATE `chatroompost` SET likecount='-11' WHERE idchatroompost=1; SELECT *FROM chatroompost;

但是我得到了

Error Code: 1442. Can't update table 'chatroompost' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.

我试过REPLACE所有AFTER至 BEFORE但仍然有同样的错误。

Answer 1

解决方案:将其设置为 BEFORE UPDATE ON 触发器，并使用 NEW 运算符，它将完成这项工作。

DROP TRIGGER IF EXISTS`chatroompost_AFTER_UPDATE` ; 
DELIMITER $$ 
use mydb $$

CREATE TRIGGER `chatroompost_AFTER_UPDATE` 
BEFORE UPDATE ON `chatroompost` 
FOR EACH ROW BEGIN  
    IF (NEW.likecount <= -5) THEN
        NEW.view='0';   
    END IF;  
END $$ 
DELIMITER ;  

原因:您无法更新调用触发器的表(聊天室帖子):

Within a stored function or trigger, it is not permitted to modify a table that is already being used (for reading or writing) by the statement that invoked the function or trigger.

这样做会产生错误 1442:

Error Code: 1442
Can't update table 'chatroompost' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.