mysql - MySQL 查询遇到问题

Question

需要生成课程列表和计数

1. 全部
2. 未答复
3. 已回答但未选中

问题。

这是我的查询

SELECT c.id, 
    c.name, 
    COUNT(allq.id) 'All', 
    COUNT(unanswered.id) 'Unanswered',
    COUNT(unchecked.id) 'Unchecked'
FROM courses c
LEFT JOIN `courses-lessons` cl 
    ON c.id = cl.cid
LEFT JOIN lesson_questions allq 
    ON cl.id = allq.lid
LEFT JOIN
(
    SELECT q.id, a.qid, q.lid
    FROM lesson_questions q
    LEFT JOIN 
    (
        SELECT id, qid
        FROM answers
        WHERE id NOT IN (SELECT aid FROM answer_chk_results)
    ) a 
        ON q.id = a.qid 
) unchecked 
    ON cl.id = unchecked.lid
LEFT JOIN
(
    SELECT id
    FROM lesson_questions
    WHERE id NOT IN (SELECT qid FROM answers)
) unanswered 
    ON cl.id = unchecked.lid
GROUP BY c.id, c.name

这是一个SQL Fiddle

数据库结构

https://docs.google.com/open?id=0B9ExyO6ktYcOenZ1WlBwdlY2R3c

我添加了 3 个问题作为示例数据，但查询计算所有问题并返回 9。这是不可能的。出了点问题。想不通，我错过了什么。

更新

我将解释一些表格：

1. answer_chk_results- 检查答案表。因此，如果此表上不存在某些答案，则表示未选中
2. lesson_questions- 课程 <-> 问题关联（按 id）表
3. courses-lessons- 课程 <-> 课程关联（按 id）表

只有第一个问题似乎并不难：当然，要计算所有问题的数量，我的计划如下所示：

1. 首先，我们需要获取所有课程名称列表。查询将如下所示：

   从课程 c 中选择 c.id、c.name

2. 然后courses-lessons通过每个选定的课程从关联表中获取所有课程1.（不知道如何继续之前的查询）

3. 然后，按所选课程 ID（列）计算所有问题lid2.

Answer 1

您可以通过使用条件计数语句来做到这一点，因此您不需要所有子查询：

SELECT  c.ID,
        c.Name,
        COUNT(DISTINCT q.ID) AS Questions,
        COUNT(DISTINCT CASE WHEN a.ID IS NULL THEN q.ID END) AS UnAnswered,
        COUNT(DISTINCT CASE WHEN cr.ID IS NULL AND a.ID IS NOT NULL THEN q.ID END) AS UnChecked
FROM    Courses c
        LEFT JOIN `Courses-Lessons` cl
            ON cl.CID = c.ID
        LEFT JOIN Lesson_Questions q
            ON cl.ID = q.LID
        LEFT JOIN Answers a
            ON a.QID = q.ID
        LEFT JOIN Answer_chk_results cr
            ON a.ID = cr.AID
GROUP BY c.ID --, c.Name

SQL小提琴

---

编辑

SELECT  c.ID,
        c.Name,
        COUNT(DISTINCT q.ID) AS Questions,
        COUNT(DISTINCT CASE WHEN a.ID IS NULL THEN q.ID END) AS UnAnswered,
        COUNT(a.ID) AS Answers,
        COUNT(DISTINCT CASE WHEN cr.ID IS NULL THEN a.ID END) AS UnChecked
FROM    Courses c
        LEFT JOIN `Courses-Lessons` cl
            ON cl.CID = c.ID
        LEFT JOIN Lesson_Questions q
            ON cl.LID = q.LID
        LEFT JOIN Answers a
            ON a.QID = q.QID
        LEFT JOIN Answer_chk_results cr
            ON a.ID = cr.AID
GROUP BY c.ID, c.Name

Answer 2

也许 - http://sqlfiddle.com/#!2/d23b4/42

SELECT  c.ID,
        c.Name,
        COUNT(q.ID) AS 'Questions',
        SUM(CASE WHEN a.ID IS NOT NULL Then 1 ELSE 0 END ) as 'Unanswered',
        SUM(CASE WHEN cr.ID IS NOT NULL Then 1 ELSE 0 END ) as 'Unchecked'
FROM    Courses c
        LEFT JOIN `Courses-Lessons` cl
            ON cl.CID = c.ID
        LEFT JOIN Lesson_Questions q
            ON cl.ID = q.LID
        LEFT JOIN Answers a         
            ON a.QID = q.ID             
        LEFT JOIN Answer_chk_results cr
            ON a.ID = cr.AID
GROUP BY c.ID