Mysql Join with 2 foreign keys in same table referencing same key

I have the 2 tables below.

Table: Users

user_id     username
--          --
1           name1
2           name2
3           name3

Table: Rel

user1       user2
--          --
1           2
3           2
1           3

My goal is to retrieve it like this :

user1       user2
--          --
name1       name2
name3       name2
name1       name3

Excuse my bad terminology and English. The user1 and user2 are foreign keys from users.user_id and together they make a composite key.

I am able to get one column as below

SELECT users.username
FROM users
JOIN rel ON rel.user1 = users.user_id

But when I try to get them together as displayed above in the goal I couldn't manage to get it working at all. If anybody have any suggestions I would be really grateful

Solution

You should really "just try something" before asking. Try this:

SELECT u1.username user1, u2.username user2
FROM rel
JOIN users u1 ON rel.user1 = u1.user_id
JOIN users u2 ON rel.user2 = u2.user_id

A most important part to note is that you MUST use "table aliases" to differentiate between the first join and the second join to the same table. "u1" and "u2" are the aliases I chose for this example.