数据库 – MySQL中的加权平均计算？

我目前正在使用以下查询来获取一些数字：

SELECT gid,count(gid),(SELECT cou FROM size WHERE gid = infor.gid)       
FROM infor 
WHERE id==4325 
GROUP BY gid;

我目前在这个阶段得到的输出如下：

+----------+-----------------+---------------------------------------------------------------+
| gid      | count(gid)      | (SELECT gid FROM size WHERE gid=infor.gid)                    |
+----------+-----------------+---------------------------------------------------------------+
|       19 |               1 |                                                            19 | 
|       27 |               4 |                                                            27 | 
|      556 |               1 |                                                           556 | 
+----------+-----------------+---------------------------------------------------------------+

我试图计算加权平均,即

(1*19+4*27+1*556)/(19+27+556)

有没有办法使用单个查询？

解决方法

使用：

SELECT SUM(x.num * x.gid) / SUM(x.cou)
  FROM (SELECT i.gid,COUNT(i.gid) AS num,s.cou
          FROM infor i
     LEFT JOIN SIZE s ON s.gid = i.gid
         WHERE i.id = 4325
      GROUP BY i.gid) x