Remove reverse duplicates from an SQL query

Question

Let\'s say that a query result is supposed to return a list of string pairs (x, y). I am trying to eliminate the reverse duplicates. What I mean is, if (x, y) was one of the

Answer 1

select e.column3, f.column3 from example as e, example as f where e.column2 = f.column2
       and e.column3 <> f.column3 where e.id < f.id

adding a simple where clause should do it.