Unique movies by UNION 两个join的结果，MYSQL

Question

我运行以下查询 UNION 对以下 4 个表的两个连接的结果：

SELECT member_CROWD.worker_Id, member_CROWD.Unreliable, Answer_CROWD.qId, Answer_CROWD.answer
FROM member_CROWD
JOIN `Answer_CROWD` 
ON member_CROWD.worker_Id = Answer_CROWD.worker_Id 
WHERE member_CROWD.Unreliable = '0' AND Answer_CROWD.qId = 'q8'
GROUP BY Answer_CROWD.answer

UNION

SELECT member.mem_id, member.Unreliable, Answer.qId, Answer.answer
FROM member
JOIN `Answer` 
ON member.mem_id = Answer.userId 
WHERE member.Unreliable = '0' AND Answer.qId = 'q8'
GROUP BY Answer.answer

这是因为我有两个实验要收集数据；一种是通过让我的朋友填写我的调查（数据存储在 member 和 Answer 表中），另一种是通过 Crowdsourcing（数据存储在 member_CROWD 和 Answer_CROWD）。

现在的问题是，我想知道例如 "Unique Number of Movies selected by users"，但来自所有用户（朋友和人群）。上面的查询可以 UNION 两个连接结果，但答案仍然不是唯一的（因为它们仅在每个连接结果中是唯一的）。

有人可以帮助我了解如何在整个实验中获得独特的#of 电影吗？

谢谢，

Answer 1

Distinct 可以是运行在 mysql 中的计数中，这非常方便。

select Count(Distinct answer) from (
SELECT member_CROWD.worker_Id, member_CROWD.Unreliable, Answer_CROWD.qId, Answer_CROWD.answer
FROM member_CROWD
JOIN `Answer_CROWD` 
ON member_CROWD.worker_Id = Answer_CROWD.worker_Id 
WHERE member_CROWD.Unreliable = '0' AND Answer_CROWD.qId = 'q8'
GROUP BY Answer_CROWD.answer

UNION

SELECT member.mem_id, member.Unreliable, Answer.qId, Answer.answer
FROM member
JOIN `Answer` 
ON member.mem_id = Answer.userId 
WHERE member.Unreliable = '0' AND Answer.qId = 'q8'
GROUP BY Answer.answer
) a

Unique movies by UNION 两个join的结果，MYSQL

Unique movies by UNION the results of two join, MYSQL

mysql

union

join