从另一个表中删除 ID 不匹配的 sql 行

Delete sql rows where IDs do not have a match from another table(从另一个表中删除 ID 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:

I have 2 tables like this:

表文件:

| 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.

我想删除表 blob 中所有在表 files.id 中找不到 fileid 的行.

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.

推荐答案

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

尽可能在事务中执行 DELETE(假设支持 - IE:不在 MyISAM 上)，以便在出现问题时可以使用回滚来恢复更改.

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.

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