带计数的SQL多重联接

我有三张桌子：

FORM(id)

QUESTION(id, form_id, text)  --> X questions for a form

ANSWER(id, question_id, answer_number, text) --> X answers for a question

我还提供了一个表格，供用户回答：

USERS_ANSWERS(id, question_id, answer_number)

我想为每个问题提供答案中给出的计数，如：

问题编号、答案编号、计数（用户回答此问题）

如果没有答案，则计数=0

你能帮我吗？花了我几个小时，我还是一无所有(

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PS：是的，我知道，为什么我不在用户答案中使用答案id？我不知道，这不是我的数据库…

你只需按（问题id，答案编号）分组，然后计数

select 
question_id, answer_number, count(answer_number) as count
from user_answers 
group by question_id, answer_number
order by question_id, answer_number

您需要从

USERS\u ANSWERS

表中获取其他两个表中每个问题和答案记录的计数

下面是一个这样做的示例，同时返回所有问题，即使这些问题没有答案：

select qst.id                       as 'question_id',
       isnull(ans.answer_number, 0) as 'answer_number',  -- isnull here because not all questions might have answers
       isnull((select count(1)
                 from USERS_ANSWERS usa
                where usa.question_id   = qst.id
                  and usa.answer_number = ans.answer_number), 0) as 'total user answers'
  from QUESTION qst
         left outer join -- left outer join here because not all questions might have answers
       ANSWER   ans on ans.question_id = qst.id

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一个简单的连接就可以了

SELECT q.id question_id, a.answer_number, COUNT(ua.id) answer_count
FROM question q
JOIN answer a 
  ON q.id = a.question_id
LEFT JOIN users_answers ua 
  ON q.id = ua.question_id AND a.answer_number = ua.answer_number
GROUP BY q.id, a.answer_number
ORDER BY q.id, a.answer_number

第一个连接将所有问题及其答案组合在一起，以获得所有有效的组合。下面的左连接计算所有组合的所有答案，允许零计数

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.

发布一点SQL努力。添加一个带有used DBMST的标记。当问题陈述时，这永远不会给出count=0。