删除ID与另一个表不匹配的SQL行
问题描述：
我正在尝试删除mysql表中的孤立条目.
I'm trying to delete orphan entries in a mysql table.
我有2张这样的桌子:
表files:
| id | ....
------------
| 1 | ....
| 2 | ....
| 7 | ....
| 9 | ....
表blob:
| fileid | ....
------------
| 1 | ....
| 2 | ....
| 3 | ....
| 4 | ....
| 4 | ....
| 4 | ....
| 9 | ....
fileid和id列可用于将表连接在一起.
The fileid and id columns can be used to join the tables together.
我要删除表blob中的所有行，其中在表files.id中找不到fileid.
I want to delete all rows in table blob where fileid cannot be found in the table files.id.
因此，使用上面的示例将删除行:3& blob表中的4(s).
So using the example above that would delete rows: 3 & 4(s) in the blob table.
答
使用LEFT JOIN/IS NULL:
DELETE b FROM BLOB b
LEFT JOIN FILES f ON f.id = b.fileid
WHERE f.id IS NULL
使用不存在:
DELETE FROM BLOB
WHERE NOT EXISTS(SELECT NULL
FROM FILES f
WHERE f.id = fileid)
使用NOT IN:
DELETE FROM BLOB
WHERE fileid NOT IN (SELECT f.id
FROM FILES f)
警告
只要有可能，就在事务中执行DELETE(假设受支持-IE:不在MyISAM上)，以便在出现问题时可以使用回滚来还原更改.
Warning
Whenever possible, perform DELETEs within a transaction (assuming supported - IE: Not on MyISAM) so you can use rollback to revert changes in case of problems.