MySQL的：你不能指定目標表「任務」的更新在FROM子句

Question

我有MySQL錯誤「您不能指定目標表‘任務’在FROM子句更新」運行下面的查詢：

DELETE FROM tasks 
WHERE tasks.id IN 
(
SELECT tasks.id 
FROM tasks 
    JOIN deadlines ON deadlines.id = deadline_id 
WHERE DATE_ADD(tasks.created_at, INTERVAL deadlines.duration DAY) <= NOW() 
) 

我該如何管理？

Thanx！

Answer 1

你可以把它包裝在像這樣的子查詢中。問題是MySQL無法更新它也在查詢的行。這將使MySQL使用一個臨時表隱式存儲你想要刪除的id。

DELETE FROM tasks 
WHERE tasks.id IN 
(
SELECT id FROM 
(
SELECT tasks.id 
FROM tasks 
    JOIN deadlines ON deadlines.id = deadline_id 
WHERE DATE_ADD(tasks.created_at, INTERVAL deadlines.duration DAY) <= NOW() 
) AS taskstodelete 
) 

Answer 2

這是因爲你不止一次地指定了任務表。試試：

DELETE FROM tasks 
USING deadlines 
WHERE deadlines.id = tasks.deadline_id 
AND DATE_ADD(tasks.created_at, INTERVAL deadlines.duration DAY) <= NOW()