MySQL 派生表中列值的总和

Question

这是我的查询:

SELECT usr.id,
       count(DISTINCT sol.id) as 'Asked',
       count(DISTINCT ans.id) as 'Answered',
       sum(DISTINCT CASE ans.accepted WHEN 1 THEN 1 ELSE 0 end) as 'Accepted'
FROM tbl_users usr
LEFT JOIN tbl_solutions sol on sol.authorID = usr.id
LEFT JOIN tbl_solution_answers ans on ans.authorID = usr.id
group by usr.id, sol.authorID

我的上述查询与 sum(DISTINCT CASE ans.accepted WHEN 1 THEN 1 ELSE 0 end) 仅返回 1，尽管我知道情况并非如此。我尝试在 ans.authorID 上添加组子句，但没有效果。

如何获取 tbl_solution_answers ans 表中所有行的总和，其中 authorID 是 tbl_users.id 和 >已接受为 1。

Answer 1

SELECT usr.id,
   count(DISTINCT sol.id) as 'Asked',
   count(DISTINCT ans.id) as 'Answered',
   count(DISTINCT case ans.accepted when 1 then ans.id end) as 'Accepted'
FROM tbl_users usr
LEFT JOIN tbl_solutions sol on sol.authorID = usr.id
LEFT JOIN tbl_solution_answers ans on ans.authorID = usr.id
group by usr.id, sol.authorID, ans.authorID

经过这么多次排列count(DISTINCT case ans.accepted when 1 then ans.id end) as 'Accepted'似乎有效。现在如果 authorID在tbl_solution_answers有 8 行，它们都将返回为 Answered如果说其中 3 个是 Accepted那么 3 返回为 Accepted .