SELECT
    [t2].[Username],
    CAST(SUM([t1].[Uploaded]) AS decimal)/CAST(SUM([t1].[Downloaded]) AS decimal) AS Ratio
FROM UserTorrentTracking t1
JOIN "User" t2 ON [t2].[Id] = [t1].[UserId]
GROUP BY t2.Username
ORDER BY Ratio DESC
OFFSET 0 ROWS -- needed for sql server 2014
FETCH FIRST 10 ROWS ONLY