How to Delete Orphan Rows in a Database Table Based on Unmatched IDs?

Delete orphans based on not matching ID

Question:

Delete

in the blob table cannot find a line of fileid. files id Table structure:

Expected results:

<code>files表：
| id | .... |
|---|---|
| 1  | .... |
| 2  | .... |
| 7  | .... |
| 9  | .... |

blob表：
| fileid | .... |
|---|---|
| 1  | .... |
| 2  | .... |
| 3  | .... |
| 4  | .... |
| 4  | .... |
| 4  | .... |
| 9  | .... |</code>

Delete The line of in the table is 3 and 4, because they have not matched the in the

table.

blob Solution: fileid files fileid <.> 1. Use left join/is null:

<.> 2. Use not exists:

<.> 3. Use not in:

DELETE b FROM BLOB b 
  LEFT JOIN FILES f ON f.id = b.fileid 
      WHERE f.id IS NULL

Warning:

DELETE FROM BLOB 
 WHERE NOT EXISTS(SELECT NULL
                    FROM FILES f
                   WHERE f.id = fileid)

To ensure that it can be rolled when there is an error, please perform the delete operation in the transaction.

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