Mysql 如何在包含左联接的其他选择查询中包含选择查询 学生表格 期间表格，此表格用于确定学生可以聚集的最大与会者人数 出勤表，学生出勤的虚拟详细信息

我找到了一个查询，可以根据性别计算学生的平均分数， 妇女：

男子：

SELECT (COUNT(a.tapping_time)/2)/p.max_session_male*100 AS 'men_score ' 
FROM period p
LEFT JOIN attendance a ON p.period_id = a.period_id
LEFT JOIN student s ON a.student_id = a.student_id
WHERE s.gender = 'male'
GROUP BY p.period_id

但是如何在一张桌子上得分呢

所需结果：

  -----------------------------------------------------------------------------
| period_id | from       | to         | total_att | women_score | men_score |
|-----------|------------|------------|-----------|-------------|-----------|
|     1     | 2018-03-02 | 2018-03-04 |    31     |     78      |     30    |
|     2     | 2018-03-05 | 2018-03-08 |    41     |     95      |     7.5   |
-----------------------------------------------------------------------------

---

使用条件聚合：

SELECT
    period_id,
    MIN(date) AS `from`,
    MAX(date) AS `to`,
    COUNT(*) AS total_att,
    100 * COUNT(CASE WHEN s.gender = 'male'
               THEN a.tapping_time END) / p.max_session_male AS male_score,
    100 * COUNT(CASE WHEN s.gender = 'female'
               THEN a.tapping_time END) / p.max_session_female AS female_score
FROM period p
LEFT JOIN attendance a
    ON p.period_id = a.period_id
LEFT JOIN student s
    ON a.student_id = a.student_id
GROUP BY p.period_id;

---

请注意，在按

period\u id

分组时，选择

max\u session\u male

和

max\u session\u female

列可能是可疑的。但是如果

period\u id

是

period

表的主键，那么就可以了。

很抱歉@Tim结果与我需要的不匹配，不能计算分数number@codefighter我更新了我的答案，使之完全符合您的预期输出。我的答案的关键仍然是使用条件聚合。学生可以聚集的最大出席人数-嗯？

SELECT (COUNT(a.tapping_time)/2)/p.max_session_female*100 AS 'women_score' 
FROM period p
LEFT JOIN attendance a ON p.period_id = a.period_id
LEFT JOIN student s ON a.student_id = a.student_id
WHERE s.gender = 'female'
GROUP BY p.period_id

SELECT (COUNT(a.tapping_time)/2)/p.max_session_male*100 AS 'men_score ' 
FROM period p
LEFT JOIN attendance a ON p.period_id = a.period_id
LEFT JOIN student s ON a.student_id = a.student_id
WHERE s.gender = 'male'
GROUP BY p.period_id

  -----------------------------------------------------------------------------
| period_id | from       | to         | total_att | women_score | men_score |
|-----------|------------|------------|-----------|-------------|-----------|
|     1     | 2018-03-02 | 2018-03-04 |    31     |     78      |     30    |
|     2     | 2018-03-05 | 2018-03-08 |    41     |     95      |     7.5   |
-----------------------------------------------------------------------------

SELECT
    period_id,
    MIN(date) AS `from`,
    MAX(date) AS `to`,
    COUNT(*) AS total_att,
    100 * COUNT(CASE WHEN s.gender = 'male'
               THEN a.tapping_time END) / p.max_session_male AS male_score,
    100 * COUNT(CASE WHEN s.gender = 'female'
               THEN a.tapping_time END) / p.max_session_female AS female_score
FROM period p
LEFT JOIN attendance a
    ON p.period_id = a.period_id
LEFT JOIN student s
    ON a.student_id = a.student_id
GROUP BY p.period_id;