mysql - 帮助处理简单的 SQL 语句

Question

我有一个用户表和 user_friend 表。user_friend 显示我和谁是朋友（所以它是 uid 和 fid）。我想获取我所有朋友的信息，所以我做了：

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

但它给了我一个子查询返回超过 1 行，我应该如何修改这个查询？

score 3 · Accepted Answer

你应该尝试像 JOIN

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

score 2 · Accepted Answer

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

或者，在 MySQL 中，我相信我记得读过连接通常比子选择快得多。所以也许：

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

score 0 · Accepted Answer

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);

score 0 · Accepted Answer

使用 IN 而不是等于：

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

score 0 · Accepted Answer

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

5 回答 5