MySQL slutter sig til to borde, find max antal og bestil efter

select daybook.userid, count(*) as count 
    from daybook, rating 
    where daybook.userid = rating.userid
    group by daybook.userid
    order by count desc

Men du har ikke engang brug for dagbogsbordet:

select userid, count(*) as count
   from rating
   group by userid
   order by count desc