＃1241 - 操作數應該包含1列（s）如何解決？

Question

好傢伙，我有與下面的查詢mysql的這個錯誤，我不知道在哪裏做的錯誤，感謝你的幫助:)

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

在您的查詢的字段列表

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 

這會將子查詢的結果用作message。

但是，子查詢選擇兩列。

Answer 2

此：

(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 

應該返回1個值，並將其返回2，這就是爲什麼出現錯誤

解決方案1：

CONCAT(p.msg_text,p.occured_at) 

解決方案2：

有2子查詢一個用於p.msg_text，另一個用於p.occured_at