DROP TRIGGER `backups`;

delimiter //
create trigger backups
before update on articles
for each row
begin
declare time int(1);
select count(id) into time from articles_backups where article_id=new.id;
if time > 5 then
delete from articles_backups where article_id=new.id order by id asc limit 1;
end if; 
end;
//
delimiter ;