Question

数据：

Programs  
- degree (name)  
- Course (course list)  

Degrees  
- code (unique identifier)  
- name  
- type (either postgrad or undergrad)  

Course  
- code (unique identifier)   
- name

因此，undergrad和postgrad学位中都开设了一些课程，我想知道如何获得所有这些课程。

Answer 1

这应该可以帮助您满足要求，

SELECT C.Name
from
Program P
inner join Degrees D
on D.Code=P.Degree and (D.Type = 'postgrad' OR D.Type = 'undergrad')
inner join Course C
on C.Code=P.Course
group by C.Name
having count(*)>1

Answer 2

一种方法是聚合：

select p.course
from program p inner join
     degrees d
     on d.Code = p.Degree
where d.type in ('postgrad', 'undergrad')
group by p.course
having count(distinct d.type) = 2;

仅在需要名称而不是代码时才需要加入course。

Answer 3

我会用2个子选择来做到这一点：

SELECT c.name
from course C 
-- at least one postgrad programs/degrees for this course
inner join (
    select distinct p.course 
    from Program P inner join Degrees D on d_pg.Code=P.Degree 
    where D.Type = 'postgrad'
) as P_pg on C.Code=P_pg.Course
-- at least one undergrad programs/degrees for this course
inner join (
    select distinct p.course 
    from Program P inner join Degrees D on d_pg.Code=P.Degree 
    where D.Type = 'undergrad'
) as P_ug on C.Code=P_ug.Course
where 1=1
;

Answer 4

我会使用交叉点：

select courses.name
from courses
inner join programs on programs.course = courses.name
inner join degrees on degrees.code = programs.degree
where degrees.type = 'UG'
intersect
select courses.name
from courses
inner join programs on programs.course = courses.name
inner join degrees on degrees.code = programs.degree
where degrees.type = 'PG';

查询如下：选择所有本科课程，并将结果与研究生课程相交。

如果只想要本科课程，可以使用except而不是相交（交换两个查询，如果只想要研究生课程，则使用except）。

SQL：如何获得同时具有本科和研究生学位的课程？

4 个答案: