Unique constraint for permutations across multiple columns

Question

Given the following three columns in a Postgres database: first, second, third; how can I create a constraint such that permutations are unique?

E.g. If (\'foo

Answer 1

Suggestion from co-worker, variation of @julien's idea:

Sort the terms alphabetically and place a delimiter on either side of each term. Concatenate them and place them in a separate field that becomes the primary key.

Why the delimiter? So that, "a", "aa", "aaa" and "aa", "aa", "aa" can both be inserted.