转子查询到连接查询

Question

对于此查询：

SELECT `user_id`, `user_name` FROM users WHERE `user_id` IN (SELECT user_one, user_two FROM friends WHERE user_one='$my_id' OR user_two = '$my_id') 

我收到此错误信息：

基数违规：1241操作数应包含1列（S）

是否有可能在连接中使用2列而不是子查询？如果是，如何？

Answer 1

为什么不使用这样的工会：如果你想重新

SELECT `user_id`, `user_name` 
     FROM users 
      WHERE `user_id` IN (SELECT user_one FROM friends 
               where user_one = '$my_id' 
           UNION 
           SELECT user_two FROM friends 
               where user_two = '$my_id') 

Answer 2

选择a.userid，从用户a.username 一个 内加入的朋友b 上a.userid = b.userid 其中b.user_one = '$添加my_id' 或b.user_two = '$添加my_id'

Answer 3

试试这个：因为IN子句不能在WHERE语句选择上多列

SELECT user_id, user_name FROM users U 
join friends F 
ON F.user_id=U.user_id 
and F.user_name=U.user_name 
WHERE F.user_one='$my_id' OR F.user_two = '$my_id' 

Answer 4

查询返回的错误。

我想你正在寻找可能是这样的

SELECT 
    user_id, 
    user_name 
FROM users INNER JOIN Friends ON Users.User_ID = User_one OR Users.User_ID = User_Two 

Answer 5

SELECT USER_ID，USER_NAME 来自用户的一个朋友b WHERE a.user_id = b.user_one AND（b.user_one = '$添加my_id' OR b.user_two = '$添加my_id'）

Answer 6

从users表，其中你的user_id是在user_one或friends表user_two线，你可以做到以下几点：

SELECT `user_id`, `user_name` 
FROM users 
WHERE `user_id` IN (
    SELECT user_one 
    FROM friends 
    WHERE user_one = '$my_id' 
) 
UNION ALL 
SELECT `user_id`, `user_name` 
FROM users 
WHERE `user_id` IN (
    SELECT user_two 
    FROM friends 
    WHERE user_two = '$my_id' 
); 

Answer 7

IN操作数只需要一个参数。如果你想得到你所有的朋友，你需要这样做，只返回一列。你可以做这样的事情与UNION：

SELECT user_one 
FROM friends 
WHERE user_two = 'me' 
UNION 
SELECT user_two 
FROM friends 
WHERE user_one = 'me'; 

然后，用它作为你的参数：

SELECT user_id, user_name 
FROM users 
WHERE user_id IN(
    SELECT user_one 
    FROM friends 
    WHERE user_two = 'me' 
    UNION 
    SELECT user_two 
    FROM friends 
    WHERE user_one = 'me');