[英]How to query a pair like table structure?
Before Query 在查询之前
User Friend
A B
A C
D A
F A
After Query 查询后
User Friend
A B
A C
A D
A F
How can I get the result shown. 如何显示结果? I want to get all friends of A.
我想得到A的所有朋友。
With a union: 与工会:
select user, friend
from t
where user = 'A'
union
select friend, user
from t
where friend = 'A'
Notice than Union
behavior is distinct
that is that you expect ( opposed to union all
) 请注意,
Union
行为distinct
您期望的不同(反对union all
)
Try this 尝试这个
SELECT USER AS 'User',
friend AS 'Friend'
FROM t
WHERE USER = 'A'
UNION
SELECT friend ,
USER
FROM t
WHERE friend = 'A'
没有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'
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