MySQL錯誤1442

Question

我有兩個表：

sanction with these attributes: DriverID , Calification , Points
people with these attributes: pID , city , TotalPoints

，我有這個觸發器：

DROP TRIGGER IF EXISTS updatePoints_tgr; 

delimiter $$ 
CREATE TRIGGER 
updatePoints_tgr AFTER UPDATE 
ON sanctions FOR EACH ROW 
BEGIN 
    if NEW.points > OLD.points 
    THEN 
     UPDATE people 
     SET TotalPoints = TotalPoints + (NEW.points - OLD.points) 
     WHERE people.pID = NEW.DriverID; 
    elseif NEW.points < OLD.points 
    THEN 
     UPDATE people 
     SET TotalPoints = TotalPoints - (NEW.points - OLD.points) 
     WHERE people.pID = NEW.DriverID; 
    END IF; 
END$$ 
delimiter ; 

，當我嘗試執行此更新

UPDATE sanctions 
JOIN people ON sanctions.DriverID=people.pID 
SET points=points+6 
WHERE city='Barcelona' AND Calification='LightPenalty' 

我得到這個錯誤：

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

我該如何解決它？謝謝。

我使用的是Windows 10和MySQL服務器5.7.17

Answer 1

不能更新，其中觸發器被調用的表（sanctions和people）：

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.

這樣做將產生錯誤1442：

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

---

你的情況下，：混亂可以是由於JOIN上sanctions和people爲UPDATE - 使得無論使用中的表中，如所述的上面的「使用」裝置「讀取或寫入」。

---

要測試 - 嘗試UPDATE查詢無JOIN（與people） - 如果它的工作原理，它肯定是這樣的。