更新MySQL觸發總和

Question

我試圖讓單元格Points_Per_Game在MySQL中使用觸發器來計算，不知道我錯過了什麼。

Points_Per_Game = Total_Points/Games Played, 


DELIMITER $$ 
CREATE TRIGGER trg_Point_Per_Game 
AFTER UPDATE ON Players 
FOR EACH ROW 
BEGIN 
UPDATE Players SET Points_Per_Game = Total_Points/Games_Played; 
END;$$ 
DELIMITER; 

玩家表：

+------------+--------------+--------------+-----------------+ 
| Name  | Games_Played | Total_Points | Points_Per_Game | 
+------------+--------------+--------------+-----------------+ 
| David  |   0 |   0 |   NULL | 
| John  |   6 |   7 |   NULL | 

的Games_Played和Total_Points列通過bash腳本每週更新一次。

Answer 1

你想要一個前更新觸發器，你需要參考的數據行：

DELIMITER $$ 
CREATE TRIGGER trg_Point_Per_Game 
BEFORE UPDATE ON Players 
FOR EACH ROW 
BEGIN 
    SET new.Points_Per_Game = (CASE WHEN new.Games_Played > 0 THEN new.Total_Points/new.Games_Played ELSE 0 END); 
END;$$ 
DELIMITER;