从SQL表中删除除了最后X个条目以外的所有内容？

Question

Is there an MySQL query which would delete all values from a table, except the latest 20 entries (ordered by id)?

So let's say I have a table notifications, where 1000 notifications reside and I want to keep only latest 20.

If SQL is not enough for this, using php is optional.

I have a few ideas how to do this, but I don't really consider them efficient.

Answer 1

You can find the latest id, store it into local variable and then delete everything below this id:

set @tmp_id := (select id from notifications order by id desc limit 20,1);
delete from notifications where id <= @tmp_id;