mysql - 我有 3 个表，如何将它们连接起来生成一个表？

Question

表a(作者表)

author_id
author_name

Table b (Post Table)

post_id
author_id

Table c (Earning Table)

post_id (post id is not unique)
post_earning

I wanted to generate a report consist of earnings per author.

author_id
author_name
total_earning (sum of earnings of all the posts by author)

The SQL Query used:

SELECT
   a.author_id,
   a.author_name,
   sum(post_earnings) as total_earnings
FROM TableA a
Inner Join TableB b on b.author_id = a.author_id
Inner Join TableC c on c.post_id = b.post_id
Group By 
   a.author_id,
   a.author_name

我得到的结果是这样的:

ID  user_login  total_earnings
2   Redstar 13.99
7   Redleaf 980.18
10  topnhotnews 80.43
11  zmmishad    39.27
13  rashel  1248.34
14  coolsaint   1.66
16  hotnazmul   9.83
17  rubel   0.14
21  mahfuz1986  1.09
48  ripon   12.96
60  KHK 27.81

总收入的总和实际上是2863.22。但是，如果我将结果表的所有值相加，我会得到 2415。问题出在哪里？可以从第一个评论中的链接下载使用的示例表。

Answer 1

SELECT
   a.author_id,
   a.author_name,
   sum(post_earnings) as total_earnings
FROM TableA a
Inner Join TableB b on b.author_id = a.author_id
Inner Join TableC c on c.post_id = b.post_id
Group By 
   a.author_id,
   a.author_name