How to choose a unique combination of SQL fields?

Question

SQL

Given:
Relationship table. Where there are fields user1, user2, relation
Task:
Select only unique combinations of these fields.
For example
, us1 / us2 / rel
Vasya / Petya / brothers - falls into the selection
Vasya / Petya / friends - does not fit, such a combination was higher in the line
Petya / Vasya / enemies - fits - there was no such combination
At the same time, I do not need all possible combinations these fields. I need only those that are written in the database, but they should not be repeated.
Just tell me where to dig - I'll handle it myself.
Thank you.

Answer 1

SELECT * FROM rel GROUP BY CONCAT(us1, '|', us2, '|', rel)

Answer 2

Temporary table with unique indexes + INSERT IGNORE

Answer 3

with t as
(
select 'Vasya' usr1, 'PETER' usr2, 'FRIENDSHIP' rel from dual
union all
select 'Vasya' usr1, 'PETIA' usr2, 'SERVICE' rel from dual
union all
select 'PETYA' usr1, 'Vasya ' usr2, 'LOVE' rel from dual
union all
select 'SEREZHA' usr1, 'Vasya' usr2, 'sympathy' rel from dual
)
select usr1, usr2, rel
from
(select usr1,
usr2,
rel,
row_number() over(partition by usr1 || usr2 order by usr1 || usr2) rn
from t)
where rn = 1