删除其中ID与另一个表不匹配的sql行

Question

我正在尝试删除mysql表中的孤立条目.

我有2个这样的表:

表files:

| id | ....
------------
| 1  | ....
| 2  | ....
| 7  | ....
| 9  | ....

表blob:

| fileid | ....
------------
| 1  | ....
| 2  | ....
| 3  | ....
| 4  | ....
| 4  | ....
| 4  | ....
| 9  | ....

该fileid和id列可以被用来连接表在一起.

我想删除表blob中fileid无法找到的表中的所有行files.id.

因此,使用上面的示例将删除表中的行:3和4(s)blob.

Answer 1

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NOT EXISTS:

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,在事务中执行DELETE(假设支持 - IE:不在MyISAM上),这样您就可以使用回滚来恢复出现问题时的更改.

Answer 2

DELETE FROM blob 
WHERE fileid NOT IN 
       (SELECT id 
        FROM files 
        WHERE id is NOT NULL/*This line is unlikely to be needed 
                               but using NOT IN...*/
      )

Answer 3

DELETE FROM blob
WHERE NOT EXISTS (
    SELECT *
    FROM files
    WHERE id=blob.id
)