如何查詢像表結構一樣的對？

Question

在查詢之前

User   Friend

A      B
A      C
D      A
F      A

查詢后

User   Friend

A      B
A      C
A      D
A      F

如何顯示結果？ 我想得到A的所有朋友。

Answer 1

與工會：

select user, friend 
from t
where user = 'A'
union 
select friend, user
from t
where friend = 'A'

請注意， Union行為distinct您期望的不同（反對union all ）

Answer 2

嘗試這個

SELECT  USER AS 'User',
        friend AS 'Friend'
FROM    t
WHERE   USER = 'A'
UNION
SELECT  friend ,
        USER
FROM    t
WHERE   friend = 'A'

Answer 3

沒有UNION

SELECT CASE WHEN [User]='A' THEN [user] ELSE [friend] END as [A], CASE WHEN [User]='A' THEN [friend] ELSE [user] END AS [Friend Of A] WHERE [user]='A' OR [friend]='A'