SQL - select students that had exams on every subject - sql

Question

I have two tables:
Exams(StudentID, SubjectID),
Subjects(SubjectID)
And want to select students that had exam on all subjects. How to do it?
Is it possible without using GROUP and COUNT?

Answer 1

You can do it in many ways. One of those:
DECLARE #students TABLE ( id INT )
DECLARE #exams TABLE ( id INT )
DECLARE #studentexams TABLE
(
studentid INT ,
examid INT
)
INSERT INTO #exams
VALUES ( 1 ),
( 2 )
INSERT INTO #students
VALUES ( 1 ),
( 2 ),
( 3 )
INSERT INTO #studentexams
VALUES ( 1, 1 ),
( 1, 2 ),
( 2, 1 )
SELECT *
FROM #students s
WHERE NOT EXISTS ( SELECT *
FROM #exams e
WHERE e.id NOT IN ( SELECT se.examid
FROM #studentexams se
WHERE se.studentid = s.id ) )
Output:
id
1

Answer 2

Is this what you're after:
--list all students
select *
from #students st
--where there isn't
where not exists
(
--any subject
select top 1 1
from #subjects su
--for which that student did not take an exam
where su.id not in
(
select subjectid
from #exams e
where studentId = st.id
)
)
Here's the full code (i.e. including sample data tables):
declare #subjects table(id bigint not null identity(1,1), title nvarchar(32))
declare #students table(id bigint not null identity(1,1), name nvarchar(32))
declare #exams table(id bigint not null identity(1,1), studentId bigint, subjectId bigint, grade nchar(1), attempt int)
insert #subjects select 'Maths' union select 'English' union select 'Geography' union select 'Computer Science'
insert #students select 'Anna' union select 'Billy' union select 'Christie' union select 'Daniel'
insert #exams select st.Id, su.Id, grade, attempt
from
(
select 'Anna' student, 'Maths' subject, 'A' grade, 1 attempt
union select 'Anna' student, 'English' subject, 'A' grade, 1 attempt
union select 'Anna' student, 'Geography' subject, 'A' grade, 1 attempt
union select 'Anna' student, 'Computer Science' subject, 'A' grade, 1 attempt
union select 'Billy' student, 'Maths' subject, 'A' grade, 1 attempt
union select 'Billy' student, 'Computer Science' subject, 'A' grade, 1 attempt
union select 'Christie' student, 'Maths' subject, 'A' grade, 1 attempt
union select 'Christie' student, 'English' subject, 'F' grade, 1 attempt
union select 'Christie' student, 'English' subject, 'E' grade, 2 attempt
union select 'Christie' student, 'English' subject, 'A' grade, 3 attempt
union select 'Daniel' student, 'Maths' subject, 'A' grade, 1 attempt
union select 'Daniel' student, 'English' subject, 'A' grade, 1 attempt
union select 'Daniel' student, 'Geography' subject, 'A' grade, 1 attempt
union select 'Daniel' student, 'Computer Science' subject, 'F' grade, 1 attempt
union select 'Daniel' student, 'Computer Science' subject, 'A' grade, 2 attempt
) x
inner join #students st on st.name = x.student
inner join #subjects su on su.title = x.subject
--list all students
select *
from #students st
--where there isn't
where not exists
(
--any subject
select top 1 1
from #subjects su
--for which that student did not take an exam
where su.id not in
(
select subjectid
from #exams e
where studentId = st.id
)
)