参加与MySQL和PHP

Question

数据我有2个表：

 TABLE USER 
ID | USER | PASSWORD 
1 | john | xxx 
2 | max | xxx 
3 | carl | xxx 
4 | marie | xxx 
5 | andy | xxx
 

TABLE FRIENDS 
ID | iduser | idfriends 
1 | 1 | 2 
2 | 1 | 3 
3 | 2 | 1 
4 | 2 | 4 
5 | 2 | 5 
6 | 2 | 3 
7 | 3 | 1

我怎样才能让所有的朋友约翰？

Answer 1

试试这个：

SELECT u.* FROM FRIENDS f 
INNER JOIN `USER` u 
ON f.idfriends=u.id 
WHERE f.iduser=1; 

Answer 2

SELECT u.user 
FROM user u 
LEFT JOIN friends f ON u.id=f.idfriends 
WHERE f.iduser = (SELECT id FROM user WHERE user = 'john');