MySQL多对一或一对多

Question

I'm a little confused and need some help on this. I have 3 tables.

User_Works_on

+---------+-------------+--+--+
| user_id | project_id  |  |  |
+---------+-------------+--+--+
|    5812 |     1938026 |  |  |
|    6390 |     1938026 |  |  |
|   32088 |     1938026 |  |  |
|   62830 |     1938026 |  |  |
|   64436 |     1938026 |  |  |
|   64441 |     1938026 |  |  |
|   77969 |     1938026 |  |  |
+---------+-------------+--+--+

Follower_works_on

+-------------+---------+
| follower_id | repo_id |
+-------------+---------+
|       64441 | 1938026 |
|       64441 |  477331 |
|       64441 |  477331 |
|        6390 | 1938026 |
|        6390 | 1529732 |
|        6390 |  477331 |
|        6390 |  477331 |
+-------------+---------+

Follows_user

+---------+-------------+
| user_id | follower_id |
+---------+-------------+
|    5812 |        6390 |
|    5812 |       10561 |
|    5812 |       37664 |
|    5812 |       51794 |
|    6390 |          58 |
|    6390 |         302 |
|    6390 |        1340 |
|    6390 |        1471 |
|    6390 |        2316 |
|    6390 |        3448 |
|   64441 |       40399 |
|   64441 |       57411 |
|   64441 |       64111 |
|   64441 |      180542 |
|   64441 |      294196 |
+---------+-------------+

The table User_works_on show the projects which a user works on. Follower_works_on shows the projects which a follower works on. Follows_users shows which users are followers of others. I want to link two projects if an id is a follower any user. ie i want to create a link between the project the user works on and the project the follower works on supposing there is a follower relationship between them.

For example:

User 5812 works on project 1938026
Follower 6390 works on project 1529732
Follower 6390 follows User 5812
Therefore there is a link between project 1938026 and 1529732.

I'm new to mysql so i'm not sure how to frame this kind of relationship. Any ideas would be great.

A result would look like this

+---------+-------------+-------------+-------------+
| User_id | project_id1 | project_id2 | Follower_id |
+---------+-------------+-------------+-------------+
|    5812 |     1938026 |     1938026 |        6390 |
|    5812 |     1938026 |     1529732 |        6390 |
+---------+-------------+-------------+-------------+

Answer 1

SELECT project_id, repo_id
FROM User_Works_on AS u
JOIN Follows_user AS fu ON u.user_id = fu.user_id
JOIN Follower_Works_on AS f ON fu.follower_id = f.follower_id

DEMO