mysql三表关联分组带where

查不出来：
SELECT e.id,e.ename,COUNT(s.id) AS total FROM enterprise e LEFT JOIN comm_port p ON e.id = p.eid LEFT JOIN sendedoutbox s  ON p.port = s.CommPort WHERE s.SendTime BETWEEN '2013-08-09 15:31:35' AND '2013-08-28 10:47:28'  GROUP BY p.eid ORDER BY total DESC


正确能查出来：
SELECT e.id,e.ename,COUNT(s.id) AS total FROM enterprise e LEFT JOIN comm_port p ON e.id = p.eid LEFT JOIN (SELECT * FROM sendedoutbox s WHERE s.SendTime BETWEEN '2013-08-09 15:31:35' AND '2013-08-28 10:47:28') s  ON p.port = s.CommPort GROUP BY p.eid ORDER BY total DESC