T-Sql查询 - 获得2列的唯一行

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.I have a set of data, with columns x and y. Thi