#1241-操作数应包含1列如何修复

Question

大家好，我在mysql中有以下查询错误，我不知道哪里出错了，感谢您的帮助：）

SELECT a.*,b.*,users.*,
    (SELECT p.msg_text,p.occured_at 
    FROM message_private p 
    WHERE p.group_id=a.group_id 
    ORDER BY p.occured_at DESC LIMIT 1) as message,
    f.countf,message.occured_at
FROM message_group a
INNER JOIN message_group b ON a.group_id=b.group_id
INNER JOIN users ON users.profile_id = b.profile_id
LEFT JOIN 
(
    SELECT COUNT(profile_id) countf, id_group
    FROM message_view
    WHERE profile_id = 'sN07X2'
    GROUP BY id_group
) f
  on f.id_group = b.group_id
WHERE a.profile_id = 'sN07X2'
    AND b.profile_id != a.profile_id 
    AND countf > 0 
ORDER BY p.occured_at DESC 
LIMIT 9

Answer 1

查询中的字段列表是

SELECT a.*,b.*,users.*,
    (SELECT p.msg_text,p.occured_at 
    FROM message_private p 
    WHERE p.group_id=a.group_id 
    ORDER BY p.occured_at DESC LIMIT 1) as message,
    f.countf,message.occured_at

这会将子查询的结果别名为message。

但是，子查询选择两列。

Answer 2

这：

 (SELECT p.msg_text,p.occured_at 
    FROM message_private p 
    WHERE p.group_id=a.group_id 
    ORDER BY p.occured_at DESC LIMIT 1) as message

应该返回1值，它返回2，这就是错误发生的原因

解决方案1:

CONCAT(p.msg_text,p.occured_at )

解决方案2:

有两个子查询，一个用于p.msg_text，另一个子查询用于p.occured_at