帮助简单的SQL语句

Question

我有一个用户表和user_friend表。 user_friend显示我与谁的朋友（所以它是uid和fid）。我想得到所有朋友的信息，所以我做了：

SELECT UID, Name FROM user WHERE UID = (SELECT FID FROM user_friend WHERE UID = 567445724);

但它给我一个Subquery返回超过1行，我应该如何修改这个查询？

Answer 1

您应该尝试像

一样加入

select u.uid,u.name 
   from user u join user_freinds uf on u.uid=uf.fid 
        where u.uid=567445724

Answer 2

SELECT UID, Name FROM user
WHERE UID IN (SELECT FID FROM user_friend WHERE UID = 567445724);`

或者，在MySQL中，我相信我记得读到联接通常比子选择更加困难。所以也许：

SELECT user.UID, user.Name FROM user, user_friend WHERE user.UID = user_friend.FID AND user_friend.UID = 567445724;

Answer 3

您必须使用in关键字。

SELECT UID, Name FROM user WHERE UID IN (SELECT FID FROM user_friend WHERE UID = 567445724);

Answer 4

使用IN而不是equals：

SELECT UID, Name FROM user WHERE UID IN (SELECT FID FROM user_friend WHERE UID = 567445724);

Answer 5

select user.uid, user.name from user, user_friends 
where user.uid=user_friends.fid 
  and user.uid=567445724