Mysql：从表中删除ID，除了选择中的行？

Question

The problem

I'm using buddypress for Wordpress it has a table for private messages in side which are thread ids for message threads. Currently there's no limit on how many messages can be in a thread.

I want to create a command that deletes all but the most recent 10 messages in a thread. Below is the logic, but I'm not sure the correct syntax to do it?

Any of you mysql geniuses know the answer?

DELETE FROM TABLEA WHERE id = X delete everything with thread ID x

EXCEPT 
(SELECT * FROM TABLEA WHERE id = X ORDER BY date_sent DESC LIMIT 10) 

Selects most recent 10 I do not wish deleted.

Answer 1

This should working:

DELETE FROM TABLEA WHERE id = X AND id NOT IN (
    SELECT TOP 10 id FROM TABLEA ORDER BY date_sent DESC
)

The sub-select of this query get the last 10 sent items. The main query have to delete the item with id X except the item is on the result of the sub-select.

Answer 2

I'm not sure how the table in buddypress works but I guess TABLEA should have its on primary key id. If TABLEA does have its own primary key id, here's my solution.

DELETE FROM TABLEA WHERE id = x AND TABLEA_id NOT IN 
    (SELECT TABLEA_id FROM TABLEA WHERE id = x ORDER BY date_sent DESC LIMIT 10)