删除一个表的所有未从另一个表引用的记录 [英] Deleting all records of a table that are not referenced from another table

问题描述

2张桌子:
items(id，...)
用户(id，item_id，...)

2 tables:
items(id, ...)
users(id, item_id, ...)

如何删除用户中未引用的项中的所有记录?

How do you delete all records in items that are not referenced from users?

推荐答案

请注意，NOT IN可能真的很慢.有时-令人惊讶的是-更快地执行以下操作:

Beware that NOT IN may be really slow. Sometimes - surpringly enough - its faster to do something like this:

DELETE FROM items WHERE id IN
(SELECT id FROM items EXCEPT SELECT item_id FROM users)

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