选择数据库表中的相互数字

Question

请朋友这是一个朋友用户的表格，所以我想为用户1和用户2选择共同的朋友。共同的朋友都是用圆圈标记的用户，我用特定的颜色对每个用户进行分组：这是我的编码：

    SELECT * FROM friends AS f5
INNER JOIN 
((SELECT one FROM friends WHERE two =  '1') AS f1,
(SELECT two FROM friends WHERE one =  '1') AS f2,
(SELECT one FROM friends WHERE two =  '2') AS m1, 
(SELECT two FROM friends WHERE one =  '2') AS m2)
ON (f1.one  = m1.one AND f2.two = m2.two ) 

我想让它显示用户1和2的共同朋友，但是当我在SQL中运行此查询时，它显示了一个空结果。我需要帮助。

Answer 1

通过f1和f2的联合选择一个的朋友，然后以相同的方式选择2的朋友，然后最后你的内部联接这两个结果：

select a.* from 
(select one as f1 from friends where two = '1'
union
select two as f2 from friends where one = '1') as a
inner join
(select one as f1 from friends where two = '2'
union
select two as f2 from friends where one = '2') as b
on a.f1 = b.f1

结果：

f1
5
6
3
4