MySQL joint deux tables, trouve le nombre maximum et ordonne par

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

Mais vous n'avez même pas vraiment besoin de la table daybook :

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