MySQL的：你不能指定目标表“任务”的更新在FROM子句

Question

我有MySQL错误“您不能指定目标表‘任务’在FROM子句更新”运行下面的查询：

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() 
) 

我该如何管理？

Thanx！

Answer 1

你可以把它包装在像这样的子查询中。问题是MySQL无法更新它也在查询的行。这将使MySQL使用一个临时表隐式存储你想要删除的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

这是因为你不止一次地指定了任务表。试试：

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