Sql “;朋友”;关系(2个表)
我有两张这样的桌子Sql “;朋友”;关系(2个表),sql,database,Sql,Database,我有两张这样的桌子 Users table id | name ------------- 1 | s1 2 | s2 3 | s3 4 | s4 5 | s5 6 | s6 friends table friendID | user_a | user_b -------------------- 1 | 1 | 2 2 | 3 | 1 3 | 4
Users table
id | name
-------------
1 | s1
2 | s2
3 | s3
4 | s4
5 | s5
6 | s6
friends table
friendID | user_a | user_b
--------------------
1 | 1 | 2
2 | 3 | 1
3 | 4 | 2
4 | 1 | 3
我想运行此查询:谁是s1的朋友?这是我当前的查询,但不起作用
select a.name
from users a, friends b
where a.id=b.user_b
and b.user_a = (select b.user_a
from friends
where a.name='s1');
在这里,您需要为每个
user\u a
和user\u b
加入用户表两次:
请尝试以下查询:
SELECT u.name
FROM Users u
JOIN friends f
ON u.id = f.user_b
JOIN Users u1
ON u1.id = f.user_a
WHERE u1.name = 's1';
结果:
╔══════╗
║ NAME ║
╠══════╣
║ s2 ║
║ s3 ║
╚══════╝
看见
编辑:在查询(您已经尝试过)中,您在子查询中使用了外部表的id和名称。所以您需要使用子表的id和名称,如下所示:
select a.name
from users a, friends b
where a.id=b.user_b
and b.user_a IN (select id
from users
where name='s1');
请参见以下内容:
SELECT DISTINCT c.name
FROM users a, friends b, users c
WHERE a.id=b.user_a
AND b.user_b=c.id
AND a.name='s1';
您正在使用哪些RDBMS?
`SELECT DISTINCT users.name
FROM users, friends
WHERE (users.id=friends.user_a OR users.id=friends.user_b )
AND (friends.user_a='1' OR friends.user_b='1')
AND (users.id!='1')`
Result:
s2
s3