MySQL:不能在FROM子句中为update指定目标表'tasks‘

Question

我在执行以下查询时遇到MySQL错误"You‘t specify target table 'tasks’for update in FROM子句“：

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()
)

我该如何管理它呢？

谢谢！

Answer 1

您可以将其包装在子查询中，如下所示。问题是MySQL不能更新它也在查询的行。这将使MySQL隐式地使用临时表来存储您想要删除的ids。

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

这是因为您多次指定了tasks表。尝试：

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