創建觸發器插入

Question

我想創建一個觸發器，它刪除任何新行我插入如果該值比數多後刪除，例如8

我嘗試這樣做：

DELIMITER | 
CREATE TRIGGER mytrigger AFTER INSERT ON mytab 
    FOR EACH ROW 
    BEGIN 
     DELETE FROM mytab WHERE myparameter > 8; 
    END 
| 

DELIMITER ; 

我想：

INSERT INTO mytab VALUES (9); 

，這是消息錯誤：

#1442 - Can't update table 'mytab' in stored function/trigger because it is already used by statement which invoked this stored function/trigger. 

也是，如果我把：

INSERT INTO mytab VALUES (4); 

它運行同樣的錯誤......

謝謝！

Answer 1

不要刪除！只是在插入時產生錯誤：

DELIMITER | 
CREATE TRIGGER mytrigger BEFORE INSERT ON mytab 
    FOR EACH ROW 
    BEGIN 
     IF new.myparameter > 8 THEN 
      signal sqlstate '45000' set message_text = 'Parameter value can be no larger than 8'; 
     END IF; 
    END 
| 

DELIMITER ;