with functions_ranked as (
select x, y, row_number() over(order by x) as rn_idx
from functions),


joined_pairs as (
select t1.x as x1, t1.y as y1, t2.x as x2, t2.y as y2
from functions_ranked t1
join functions_ranked t2
on t1.rn_idx != t2.rn_idx
and t1.x = t2.y
and t1.y = t2.x)

select distinct x1, y1
from joined_pairs
where x1<=y1
order by x1