SQL-基于同一表中的多个条目进行选择？

Question

如果我的表是这样设置的：

Apply: studentID, cName

Student: studentID, sName

如何从“学生”中列出“学生ID”和“ sName”，其中“应用”中有以下条目：

Apply.studentID = Student.studentID AND Apply.cName = "College1"

AND

Apply.studentID = Student.studentID AND Apply.cName = "College2"

最终，我想做的是用cNames“ College1”和“ College2”列出同时申请这两家大学的学生。

Answer 1

通过执行两个子查询，一个获得适用于College1的StudentID，另一个获得有关College2的查询，您可以确保从Student返回的学生具有两个子查询结果集中都存在的studentID。

SELECT sName
FROM Student 
WHERE studentID IN (
    SELECT DISTINCT studentID FROM Apply WHERE cName='College1'
)
AND studentID IN (
    SELECT DISTINCT studentID FROM Apply WHERE cName='College2'
)

Answer 2

您可以检查两个条件是否存在：

select * from Student s
where exists 
(select * from Apply a where a.StudentId = s.StudentId and a.cName = 'College1') and
exists 
(select * from Apply a where a.StudentId = s.StudentId and a.cName = 'College2');

Answer 3

您可以使用CTE来避免重复代码。

with
    cte
as
(
    select
        studentID
    from
        [Apply]
    where
        cName   in('College1', 'College2')
)
select
    s.sName
from
    cte
inner join
    Student s
on
    cte.studentID = s.studentID;