Question

我想计算参加2门特定课程的学生人数（crn）我可以显示所说的sids但由于某种原因我无法计算它们。

我想显示服用crn = 12345和crn = 20976

的学生人数

这是我的表

  sid  |  crn  | grade
 12321 | 12345 |   A
 12321 | 20976 |   B
 21008 | 12345 |   C
 21008 | 20976 |   A
 21008 | 28469 |   D
 21090 | 12345 |   C
 21090 | 20976 |   F

这是可行的代码

 select sid from takes where crn in (12345 , 20976 ) group by sid HAVING COUNT(*) = 2

这是我试过的代码

 select count(sid) from takes where crn in (12345 , 20976 ) group by sid HAVING COUNT(*) = 2

 select sid, count(sid) from takes where crn in ( '12345', '20976') GROUP By sid HAVING count(*) > 1

 select count(sid) from takes where (select sid from takes where crn in ( '12345', '20976') GROUP By sid HAVING count(*) > 1 )

 select sid, count(sid) from takes where (select sid from takes where crn in ( '12345', '20976') HAVING count(*) > 1 ) GROUP BY sid

所以这是我的问题，我怎么能让这个东西工作？我的意思是说某些代码可以计算它可以显示的内容并显示该数字

Answer 1

你需要一个子查询：

select count(*)
from (select sid
      from takes
      where crn in (12345 , 20976 )
      group by sid 
      having count(*) = 2
     ) s;

使用同一列的多个条件计数

1 个答案: