DISTINCT column combination with permutations

This looks more like a stack overflow question yet Union will give a distinct combination.

SELECT concat("from",':',"to") as res From Table
UNION
SELECT concat("to",':',"from") From Table

You can also use least() and greatest() together with distinct. That would preserve the individual values without the need to concatenate them.

select distinct least("from", "to"), greatest("from", "to")
from the_table;