php - Delete MYSQL values past the most recent 80 -

i'm using:

select * users order date_time desc limit 0, 80 

to display 80 recent usernames, how can make query such deletes other entries past 80?

i presume need cron job, kind of query need execute?

here different ways:

delete users users left join (   select id users order date_time desc limit 0, 80) t1 on users.id=t1.id t1.id null 

sql fiddle demo

and without limit:

delete users users left join (   select id ( select  id,          @currow := @currow + 1 row_number    users,(select @currow := 0) r order date_time desc) t row_number<=80 ) t1 on users.id=t1.id t1.id null 

sqlfiddle demo