sql - 如何根据SQL Server select语句中的两列值返回一个值？

Question

请参阅下文以了解我想要的内容:

------------------------------
   Friend       | User 
------------------------------
     2          |  1 
     3          |  2 
     2          |  5
     4          |  2 
------------------------------

当我搜索值2时，我希望搜索结果返回Friend和User中的相关值，如下所示:

--------------------------
      Friends of 2 
--------------------------
        1   - (from column User ) 
        3   - (from column Friend) 
        5   - (from column user ) 
        4   = (from column friend )  

我想要如下所示的一列搜索结果:

--------------------------
      Friends of 2 
--------------------------
        1  
        3   
        5   
        4   

如何通过在 SQL Server 中使用 SELECT 查询来实现此目的？

Answer 1

SELECT Friend FROM MyTable WHERE User = 2
UNION
SELECT User FROM MyTable WHERE Friend = 2;