EXPLAIN SELECT cem.Username, SUM(cem.ThumbsUp) AS thumbsup
FROM tbl_cnt_contestentrycomments cem, tbl_cnt_contestentries ce, tbl_cnt_contests c
WHERE cem.EntryID = ce.ID AND ce.ContestID = c.ID AND c.Startdate='2007-07-26' AND c.Enddate='2007-08-05'
GROUP BY cem.Username ORDER BY thumbsup DESC LIMIT 0,20

1, 'SIMPLE', 'cem', 'index', 'idx_entryid', 'idx_username', '452', '', 106954, 'Using temporary; Using filesort'
1, 'SIMPLE', 'ce', 'eq_ref', 'PRIMARY,idx_contestid', 'PRIMARY', '152', 'cem.EntryID', 1, ''
1, 'SIMPLE', 'c', 'eq_ref', 'PRIMARY', 'PRIMARY', '4', 'ce.ContestID', 1, 'Using where'