MySQL: You can't specify target table 'tas

问题:

I have got MySQL error "You can't specify target table 'tasks' for update in FROM clause" running the following query:

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()
)

How can I manage this?

Thanx!

回答1:

You can wrap it in a subquery like so. The issue is that MySQL can't update rows that it's also querying. This will make MySQL use a temporary table implicitly to store the ids you want to delete.

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
)

回答2:

It's because you're specifying the tasks table more than once. Try:

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