Mysql使用SELECT CONCAT结果作为条件在相同的查询

Question

我想使用这个查询，我需要在比较前连接字符串以获得正确的结果。查询正在运行，但未找到任何结果。我相信问题是当我尝试比较WHERE条款中的“myname”时。任何想法是什么正确的查询呢？

SELECT * 
FROM (SELECT CONCAT('tm_',name) AS myname FROM room) room, users 
WHERE user_name = myname; 

Answer 1

为什么不是

SELECT * FROM users,room where user_name=concat('tm_',name); 

？

Answer 2

试试这个

SELECT * 
FROM 
(
    SELECT CONCAT('tm_',name) AS myname 
    FROM room 
) t 
WHERE user_name = myname 

可能是你需要JOIN其他表users像这样：

SELECT * 
FROM 
(
    SELECT CONCAT('tm_',name) AS myname 
    FROM room 
) t 
INNER JOIN users u ON ... --some join condition 
WHERE user_name = myname 

或者：

SELECT * 
FROM 
(
    SELECT CONCAT('tm_',name) AS myname 
    FROM room 
) t, users 
WHERE t.user_name = myname"