(一)、根据teacher_no统计星期的上课数

1. -- 解法一
   
2. SELECT
   
3.   t1.teacher_no,
   
4.   (CASE WEEK WHEN '1' THEN keshu ELSE 0 END ) 礼拜一,
   
5.   (CASE WEEK WHEN '2' THEN keshu ELSE 0 END ) 礼拜二,
   
6.   (CASE WEEK WHEN '3' THEN keshu ELSE 0 END ) 礼拜三
   
7. FROM
   
8. (
   
9.     SELECT
   
10.       teacher_no,
    
11.       WEEK,
    
12.       COUNT(1) AS keshu
    
13.       FROM teach
    
14.   GROUP BY teacher_no,WEEK
    
15.  )t1
    
16.   GROUP BY t1.teacher_no;
    
17. 
    
18. 
    
19. -- 解法二 就是count()函数作用
    
20. SELECT
    
21.   t1.teacher_no,
    
22.   (CASE WEEK WHEN '1' THEN keshu ELSE 0 END ) 礼拜一,
    
23.   (CASE WEEK WHEN '2' THEN keshu ELSE 0 END ) 礼拜二,
    
24.   (CASE WEEK WHEN '3' THEN keshu ELSE 0 END ) 礼拜三
    
25. FROM
    
26. (
    
27.   SELECT
    
28.   t.teacher_no,
    
29.   t.WEEK,
    
30.   COUNT(t.keshu) AS keshu
    
31.   FROM
    
32.       (
    
33.       SELECT
    
34.       teacher_no,
    
35.       WEEK,
    
36.       '1' keshu
    
37.       FROM teach )t
    
38.   GROUP BY teacher_no,WEEK
    
39.     )t1
    
40. GROUP BY t1.teacher_no
    
41. ;

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