sum之后结果是所需要的二倍?
本人想在mysql里inner   join两个表,   两个表在join之前分别自动sum出某个字段的和:
/*   ALGORITHM=UNDEFINED   */   select   `view_essaybyuserid`.`user_id`   AS   `user_id`,`view_essaybyuserid`.`username`   AS   `username`,sum(`view_essaybyuserid`.`score`)   AS   `essay_score`,sum(`view_quizbyuserid`.`score`)   AS   `quiz_score`   from   (`wcv102`.`view_essaybyuserid`   join   `wcv102`.`view_quizbyuserid`)   where   (`view_essaybyuserid`.`user_id`   =   `view_quizbyuserid`.`user_id`)   group   by   `view_essaybyuserid`.`user_id`

问题是出来的sum结果居然都是所需要的二倍.
请高手指教如何解决.   谢谢!

------解决方案--------------------
这应该是两表交叉导致的，最简单解决方法就是直接除以2，sum(aaa)/2。
这是一种治标不治本的方法，仅供参考。(*^__^*)
------解决方案--------------------
select a.user_id,a.username,sum(a.score) AS essay_score,sum(b.score) AS quiz_score
from `wcv102`.`view_essaybyuserid` as a inner join `wcv102`.`view_quizbyuserid` as b
on a.user_id = b.user_id group by a.user_id

这样不行?