Mysql join 多張表時查詢結果出了問題

因為公司產品的需求，現在要去實現一個功能，表A放的用戶的基本信息，表B存的A表中用戶的一些行為，表C和表B的性質一樣。要求查詢的時候可以依照B表或C表中的count結果進行排序，於是就想到了join，可是出現了問題。

先貼出3張表的資料結構

<code>  CREATE TABLE `A` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(255) default NULL,
  PRIMARY KEY  (`id`),
) ENGINE=MyISAM AUTO_INCREMENT=1;</code>

<code>  CREATE TABLE `B` (
  `id` int(11) NOT NULL auto_increment,
  `userid` int(11) default NULL,
  `dosomething` varchar(255) default NULL,
  PRIMARY KEY  (`id`),
  KEY `userid` USING BTREE (`userid`)
) ENGINE=MyISAM AUTO_INCREMENT=1;</code>

<code>  CREATE TABLE `C` (
  `id` int(11) NOT NULL auto_increment,
  `userid` int(11) default NULL,
  `dosomething` varchar(255) default NULL,
  PRIMARY KEY  (`id`),
  KEY `userid` USING BTREE (`userid`)
) ENGINE=MyISAM AUTO_INCREMENT=1;</code>

自己做嘗試，發現查詢結果不一樣

<code>SELECT u.id, COUNT(s.id) AS sapply, COUNT(uu.id) AS ftotal FROM A AS u
 RIGHT JOIN B AS s ON u.id = s.userid
 RIGHT JOIN C AS uu ON u.id = `uu`.`userid`
 GROUP BY `u`.`id` ORDER BY `ftotal` DESC LIMIT 10</code>

資料明顯有問題，分開關聯看結果

<code>SELECT u.id, COUNT(s.id) AS sapply FROM A AS u
 RIGHT JOIN B AS s ON u.id = s.userid
 GROUP BY `u`.`id` ORDER BY `sapply` DESC LIMIT 10</code>

<code>SELECT u.id, COUNT(uu.id) AS ftotal FROM A AS u
 RIGHT JOIN C AS uu ON u.id = uu.userid
 GROUP BY `u`.`id` ORDER BY `ftotal ` DESC LIMIT 10</code>

大家幫忙看看，這問題出在哪呢 第一條Sql語句也沒有錯誤但是結果就是不對。