Question

I have a set of data, with columns x and y. This set contains rows where, for any 2 given values, A and B, there is a row with A and B in columns x and y respectivly and there will be a second row with B and A in columns x and y respectivly.

E.g

        **Column X**            **Column Y**
Row 1        A                       B
Row 2        B                       A             

• There are multiple pairs of data in
  this set that follow this rule.
• For every row with A, B in Columns
  X and Y, there will always be a
  row with B, A in X and Y
• Columns X and Y are of type int

I need a T-Sql query that given a set with the rules above will return me either Row 1 or Row 2, but not both.

Either the answer is very difficult, or its so easy that I can’t see the forest for the trees, either way it’s driving me up the wall.

Answer 1

Add to your query the predicate,

where X < Y

and you can never get row two, but will always get row one.

(This assumes that when you wrote “two given values” you meant two distinct given values; if the two values can be the same, add the predicate where X <= Y (to get rid of all “reversed” rows where X > Y) and then add a distinct to your select list (to collapse any two rows where X == Y into one row).)

In reply to comments:

That is, if currently your query is select foo, x, y from sometable where foo < 3; change it to select foo, x, y from sometable where foo < 3 and x < y;, or for the the second case (where X and Y are not distinct values) select distinct foo, x, y from sometable where foo < 3 and x <= y;.