Deleting a few records from SQL

[legend986]

I have four columns which look like:

A | B | C | D

A,B is a pair and C,D is another pair. I want to delete those records where P,Q,R,S repeat as R,S,P,Q. For example, if i have the data as:

1 | 2 | 3 | 4
5 | 6 | 7 | 8
3 | 4 | 1 | 2

Then I want to delete the third row because it is similar to first row. Is there a query that can do this or do I have to go down to script level coding?

[laserlight]

hmm... why are A,B and C,D pairs to begin with?

[legend986]

Well, not due to a special reason or something. They represent nodes in my problem. So a link from A,B to C,D is same as a link from C,D to A,B... So I don't want such duplicates...