Question

I have a table with data that I don’t need to keep for very long, so every night I want to remove all rows except the last 20.

To do that, I found the following query:

DELETE FROM Table WHERE ID NOT IN (
    SELECT id FROM (
        SELECT TOP 10 ID FROM Table
    ) AS x
)

MySQL doesn’t support the TOP function, so I rewrote it to use LIMIT instead:

DELETE FROM Table WHERE ID NOT IN (
    SELECT id FROM (
        SELECT ID FROM Table ORDER BY ID DESC LIMIT 10
    ) AS x
)

Unfortunately, MySQL doesn’t seem to support the LIMIT function within subqueries. So what do I do now?

How do I select all except the 10 rows with the highest ID?

I could probably just delete all the records that are older than a day or something, but it feels like I should be able to do it this way.

Answer 1

Another way:

DELETE t
FROM 
    TableX AS t
  CROSS JOIN
    ( SELECT Id
      FROM TableX
      ORDER BY Id DESC
      LIMIT 1 OFFSET 9
    ) AS tenth
WHERE t.Id < tenth.id