“Friend” relationships between 2 tables

PROBLEM

---

I have two tables like this

Users table
id    | name
-------------
1     |  s1
2     |  s2
3     |  s3
4     |  s4
5     |  s5
6     |  s6

friends table
friendID | user_a | user_b
--------------------
1        |   1    |   2
2        |   3    |   1
3        |   4    |   2
4        |   1    |   3

I want to run this query: Who is friends with s1?

SOLUTION

---

SELECT DISTINCT c.name
FROM users a, friends b, users c
WHERE a.id=b.user_a
    AND b.user_b=c.id
    AND a.name='s1';

Result:

╔══════╗
║ NAME ║
╠══════╣
║ s2   ║
║ s3   ║
╚══════╝