Delete N number of old records from table in mysql

Question

I have a LoginTime table like this:

id | user_id | datetime
1  |   1     | 2011-01-19 18:51:01
2  |   1     | 2011-01-19 18:51:02  
3  |   1             


        

Answer 1

delete LoginTime
from 
  LoginTime

left join
  (
    select id
    from LoginTime
    where user_id=1
    order by datetime desc
    limit 5
  ) as not_to_delete
on LoginTime.id=not_to_delete.id

left join
  (
    select id
    from LoginTime
    where user_id=1
  ) as existance
on LoginTime.id=existance.id

where
  not_to_delete.id is null and existance.id is not null;