如何删除Oracle中具有不同列的重复记录？

Question

我在删除具有不同列的行中的重复数据时遇到问题：

SELECT   p1, p2

  FROM   (SELECT   'A' AS p1, 'B' AS p2 FROM DUAL
          UNION
          SELECT   'B' AS p1, 'A' AS p2 FROM DUAL) a;

，结果将是：

P1 P2 
-- -- 
A , B  
B , A  

我只需要A，B或B，A

Answer 1

SELECT   distinct least(p1, p2), greatest(p1, p2)
  FROM   (SELECT   'A' AS p1, 'B' AS p2 FROM DUAL
          UNION
          SELECT   'B' AS p1, 'A' AS p2 FROM DUAL) a;