Question

码
用户
codes_users

codes包含应分配给特定users的代码codes_users保存连接信息。

SELECT users.*, 
       codes.code 
FROM   users 
       LEFT JOIN (codes 
                  INNER JOIN codes_users 
                          ON codes.id = codes_users.code_id) 
              ON users.id = codes_users.user_id

我已经设法在这个小提琴中显示代码：http://sqlfiddle.com/#!2/acd0cb/1

但是当我想计算下载时，我只得到一个结果：

SELECT users.*, 
       codes.code, 
       Sum(users.downloads) AS _downloadscount 
FROM   users 
       LEFT JOIN (codes 
                  INNER JOIN codes_users 
                          ON codes.id = codes_users.code_id) 
              ON users.id = codes_users.user_id

http://sqlfiddle.com/#!2/acd0cb/2

我也想拥有每个用户的下载次数

Answer 1

您的查询最后需要一个小组，告诉DB您希望计算每个用户

SELECT users.*, 
       codes.code, 
       Sum(users.downloads) AS _downloadscount 
FROM   users 
       LEFT JOIN (codes 
                  INNER JOIN codes_users 
                          ON codes.id = codes_users.code_id) 
              ON users.id = codes_users.user_id 
GROUP  BY users.id;

Answer 2

    SELECT users.*, codes.code, SUM(users.downloads) AS _downloadscount FROM users
LEFT JOIN
    (codes INNER JOIN codes_users ON codes.ID = codes_users.code_id)
     ON users.ID = codes_users.user_id
group by users.id

具有m / n关系表的内连接和某列的总和

2 个答案: