select R.* from Ratings R INNER JOIN (select Account, max(mRating) as MaxRatingForAccount from Ratings GROUP BY Account) Mx 
ON R.Account = Mx.Account and R.mRating = Mx.MaxRatingForAccount

there's some stuff in here that I haven't used before, like R.* and INNER JOIN and also Mx ON R. etc.,
so it's a little bit hard for me to debug it. Thanks. Steve