MySQLは2つのテーブルを結合し、最大数を見つけて順序付けます

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

しかし、実際には日記の表は必要ありません：

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