选择与特定记录相关但没有其他记录相关的记录

Question

对于多对多关系，例如班级和学生，我想选择完全具有给定成员资格的所有Classes。

Students         Classes        StudentClass
=========       ============    =================
id              id              student     class
--              ---             --------   -------
1               1               1           1
2               2               2           1
3                               3           1
4                               1           2
5                               2           2             
                                3           2
                                4           2

使用示例数据，如果我给查询S1，S2，S3-它应该只返回Class 1，而排除Class 4，因为它包含一个额外的学生。

Answer 1

以下是使用conditional aggregation的一种选择：

select class
from studentclass
group by class
having count(case when student in (1,2,3) then 1 end) = 3
   and count(*) = 3

• Online Demo

Answer 2

SQL HERE

您可以按照以下步骤进行操作：

select class from StudentClass
where class in(
    select class from StudentClass where student in(1,2,3) 
    group by class having count(distinct student)=3
) group by class
having count(distinct student)=3