When you ran this query,
what was it that wasn't right about it?
Well, it seems to think
that each student is his or
her own roommate, and it lists each pair
of roommates twice in alternating order.
There are a lot of ways to fix this,
but here's just one of them.
By asking only for the rows where
this id, is less than that id.
We eliminate the rows where they're
equal, in other words the same student.
And, we eliminate one out
of each pair of duplicates.