What will be the query to get Student names for every individual study group? - sql

Question

meetings which looks like this:
meeting_ID
place
1
A
2
B
3
C
study_groups which looks like this:
study_group_id
meeting_id (fk)
topic
1
1
Basics
2
2
Photography
3
1
Film
students which looks like this:
student_id
name
1
xyz
2
abc
2
pqr
group_members which looks like this:
study_group_id (fk)
student_id (fk)
2
10
1
1
2
5
3
15
1
9
3
2
3
11
A meeting has many study_groups and each study_groups has many students.
I want to find the student names in each group individually for meeting_id = 1.
Is that possible or not to do in the same query?
If not what should I do, please suggest me.
This is my present SQL query:
SELECT
study_groups.study_group_id,
(SELECT COUNT(*)
FROM group_members
WHERE study_groups.study_group_id = group_members.study_group_id) AS no_of_students,
study_groups.topic
FROM
study_groups
WHERE
study_groups.meeting_id = 1;
Now the table looks like:
study_group_id
no_of_student
topic
1
2
Basics
2
3
Photography
student_name column result in below is demo but I want the data as like this.
The result I expect:
study_group_id
no_of_student
topic
student_name
1
2
Basics
xyz, abc, pqr
2
3
Photography
abc, pqr

Answer 1

If you want the students in the study group and you are using Postgres, you can aggregate them into an array:
SELECT sgs.study_group_id,
(SELECT ARRAY_AGG(s.name)
FROM group_members gm JOIN
students s
ON gm.student_id = s.student_id
WHERE sg.study_group_id = gm.study_group_id
) AS student_names,
sg.topic
FROM study_groups sg
WHERE sg.meeting_id = 1;