Use Analytical function to achieve this:
select user_id, ref_id, name, ref from
(SELECT u.user_id, r.ref_id, u.name, r.ref, dense_rank() over (order by u.user_id) rn
FROM user_table u
INNER JOIN user_ref_asso ur
ON ur.user_id = u.user_id
INNER JOIN REF r
ON r.ref_id = ur.ref_id
order by u.user_id, r.ref_id)
WHERE rn <= 2;
Output:
| USER_ID | REF_ID | NAME | REF | RN |
|---------|--------|-------|------|----|
| 1 | 1 | Name1 | Ref1 | 1 |
| 1 | 2 | Name1 | Ref2 | 1 |
| 2 | 1 | Name2 | Ref1 | 2 |
| 2 | 2 | Name2 | Ref2 | 2 |