How to do the join strategy in this case? - mysql

Question

This is the situation I'm dealing with:
I have 4 tables:
Users table:
+----+-------+
| id | name |
+----+-------+
| 1 | name1 |
| 2 | name2 |
| 3 | name3 |
+----+-------+
Assignment table:
+----+-----------------+
| id | assignment_name |
+----+-----------------+
| 11 | name1 |
| 12 | name2 |
| 13 | name3 |
+----+-----------------+
Submissions:
+----+---------------+---------+
| id | assignment_id | user_id |
+----+---------------+---------+
| 1 | 11 | 3 |
| 2 | 12 | 1 |
| 3 | 11 | 2 |
+----+---------------+---------+
Group_submissions
+----+----------------+---------+
| id | submission_id | user_id |
+----+----------------+---------+
| 1 | 1 | 1 |
| 2 | 1 | 2 |
| 3 | 3 | 1 |
+----+----------------+---------+
The submission table has an assignment_id to tell in which assignment the submission belongs to.
Also users can submit a group submission, where the one that does the submission goes to the submissions table, while the others go to the group_submissions table. That way it will be counted as one submission instead of being 2,3...N submission based on how many people where in the group.
How can i get the users that have submitted a submission or have participated in a group submission in a given assignment?
The result should return the user or users that have are in the submissions table or in the group_submissions table based on a assignment id
The result should look something likes this:
+----+-------+
| id | name |
+----+-------+
| 1 | name1 |
| 2 | name2 |
+----+-------+
It should basically return the user table.
This is what i have tried so far:
This only gives me the users that aren't in the submissions table but are in the group_submission
select * from users u
right join group_submissions gs on u.id = gs.student_id
right join assignment_submissions ass on gs.submission_id = ass.id
inner join assignments a on a.id = ass.assignment_id
where a.id = number
This only gives me the one user that made the submission (in the submissions table)
select * from users u
right join assignment_submissions ass on u.id= ass.student_id
right join group_submissions gs on ass.id = gs.submission_id
inner join assignments a on a.id = ass.assignment_id
where a.id = number
What should my join strategy be here? Or maybe joins are not the right option here.
NOTE: This is a MySQL database.

Answer 1

You could use exists:
select u.*
from users u
where
exists (
select 1
from submissions s
where s.user_id = u.id and s.assignment_id = ?
)
or exists (
select 1
from group_submissions gs
inner join submissions s on s.id = gs.submission_id
where gs.user_id = u.id and s.assignment_id = ?
)

Answer 2

I am thinking a union could do it. Like this
select * from
(
select u.*, assignment_id, 'assignment_submissions' as type from users u
inner join assignment_submissions ass on u.id= ass.student_id
union
select u.*, assignment_id, 'group_submissions' from users u
inner join group_submissions gs on u.id = gs.student_id
inner join assignments a on a.id = ass.assignment_id
)a
where assignment_id = ?