student表格，| student_id | name | gender |
|------------|--------|---------|
| 1174 | Steve | male |
| 1175 | Jane | female |
| 1176 | Mark | male |
| 1177 | Lily | female |
---------------------------------
period表，此表用于确定学生可以收集的最大与会者人数| period_id | from | to | max_session_female | max_session_male |
|-----------|------------|------------|--------------------|------------------|
| 1 | 2018-03-02 | 2018-03-04 | 14 | 15 |
| 2 | 2018-03-05 | 2018-03-08 | 20 | 20 |
|-----------------------------------------------------------------------------|
attendance表，学生出勤的虚拟细节| student_id | period_id | date | tapping_time | session |
|------------|-----------|------------|--------------|---------|
| 1174 | 1 | 2018-03-02 | 15:30:49 | C |
| 1174 | 1 | 2018-03-02 | 19:56:15 | F |
| 1174 | 1 | 2018-03-03 | 05:10:20 | E |
| 1174 | 1 | 2018-03-03 | 12:28:54 | B |
| 1174 | 1 | 2018-03-03 | 15:31:12 | C |
| 1174 | 1 | 2018-03-04 | 12:26:33 | B |
| 1174 | 1 | 2018-03-04 | 15:39:06 | C |
| 1174 | 1 | 2018-03-04 | 18:32:40 | E |
| 1174 | 1 | 2018-03-04 | 19:56:09 | F |
| 1174 | 2 | 2018-03-05 | 05:14:55 | E |
| 1175 | 2 | 2018-03-05 | 12:27:29 | B |
| 1175 | 2 | 2018-03-05 | 19:53:19 | F |
| 1175 | 2 | 2018-03-06 | 12:25:45 | B |
| 1175 | 2 | 2018-03-08 | 12:29:41 | B |
| 1175 | 2 | 2018-03-08 | 15:32:14 | E |
| 1175 | 2 | 2018-03-08 | 20:24:03 | F |
| 1175 | 1 | 2018-03-02 | 05:15:13 | C |
| 1175 | 1 | 2018-03-02 | 12:36:19 | B |
| 1175 | 1 | 2018-03-02 | 15:38:20 | C |
| 1175 | 1 | 2018-03-02 | 19:52:09 | F |
| 1175 | 1 | 2018-03-03 | 05:14:24 | C |
| 1175 | 1 | 2018-03-03 | 12:29:26 | B |
| 1175 | 1 | 2018-03-03 | 15:31:48 | C |
| 1175 | 1 | 2018-03-03 | 19:55:41 | F |
| 1175 | 1 | 2018-03-04 | 12:29:52 | B |
| 1175 | 1 | 2018-03-04 | 15:40:39 | C |
| 1175 | 1 | 2018-03-04 | 19:53:18 | F |
| 1175 | 2 | 2018-03-05 | 05:12:05 | A |
| 1175 | 2 | 2018-03-05 | 12:29:27 | B |
| 1175 | 2 | 2018-03-05 | 15:28:16 | C |
| 1175 | 2 | 2018-03-05 | 19:55:52 | F |
| 1175 | 2 | 2018-03-06 | 05:15:10 | A |
| 1175 | 2 | 2018-03-06 | 12:32:10 | B |
| 1175 | 2 | 2018-03-06 | 15:33:11 | C |
| 1175 | 2 | 2018-03-06 | 20:13:48 | F |
| 1175 | 2 | 2018-03-07 | 05:13:25 | A |
| 1175 | 2 | 2018-03-07 | 12:28:13 | B |
| 1175 | 2 | 2018-03-07 | 15:37:28 | C |
| 1175 | 2 | 2018-03-07 | 20:23:06 | F |
| 1175 | 2 | 2018-03-08 | 05:11:47 | A |
| 1175 | 2 | 2018-03-08 | 12:31:43 | B |
| 1175 | 2 | 2018-03-08 | 15:28:29 | C |
| 1175 | 2 | 2018-03-08 | 20:21:29 | F |
| 1176 | 2 | 2018-03-07 | 20:50:43 | F |
| 1176 | 2 | 2018-03-08 | 19:54:32 | F |
| 1177 | 1 | 2018-03-02 | 05:13:30 | A |
| 1177 | 1 | 2018-03-02 | 12:38:29 | B |
| 1177 | 1 | 2018-03-02 | 19:53:38 | F |
| 1177 | 1 | 2018-03-03 | 05:12:33 | A |
| 1177 | 1 | 2018-03-03 | 12:34:48 | B |
| 1177 | 1 | 2018-03-03 | 15:39:05 | C |
| 1177 | 1 | 2018-03-03 | 20:00:51 | F |
| 1177 | 1 | 2018-03-04 | 05:10:59 | A |
| 1177 | 1 | 2018-03-04 | 12:33:56 | B |
| 1177 | 1 | 2018-03-04 | 15:39:09 | C |
| 1177 | 1 | 2018-03-04 | 19:48:59 | F |
| 1177 | 2 | 2018-03-05 | 05:12:15 | A |
| 1177 | 2 | 2018-03-05 | 12:30:53 | B |
| 1177 | 2 | 2018-03-05 | 15:34:53 | C |
| 1177 | 2 | 2018-03-05 | 19:53:19 | F |
| 1177 | 2 | 2018-03-06 | 05:12:56 | A |
| 1177 | 2 | 2018-03-06 | 12:30:03 | B |
| 1177 | 2 | 2018-03-06 | 15:31:00 | C |
| 1177 | 2 | 2018-03-06 | 19:52:40 | F |
| 1177 | 2 | 2018-03-07 | 05:12:30 | A |
| 1177 | 2 | 2018-03-07 | 12:34:48 | B |
| 1177 | 2 | 2018-03-07 | 15:40:34 | C |
| 1177 | 2 | 2018-03-07 | 19:53:47 | F |
| 1177 | 2 | 2018-03-08 | 05:11:21 | A |
| 1177 | 2 | 2018-03-08 | 12:35:21 | B |
| 1177 | 2 | 2018-03-08 | 15:36:26 | C |
| 1177 | 2 | 2018-03-08 | 19:52:32 | F |
我找到了一个根据性别计算学生平均分数的查询， 女人：
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
男士：
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
但如何在表格中得分？
期望的结果：
-----------------------------------------------------------------------------
| 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 |
-----------------------------------------------------------------------------
答案 0 :(得分：0)
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max_session_male分组时选择max_session_female和period_id列可能会产生疑问。但如果period_id是period表的主键，则表示没问题。