＃1247 - 參考 'SID' 不支持（參照組功能）

Question

（參照組功能） -

SELECT `subject`, 
GROUP_CONCAT(`student_id` SEPARATOR ',') as sid, 
(SELECT concat(fname,' ',surname) 
FROM student_registration 
WHERE student_id IN (sid)) as name 
FROM `email` GROUP BY `subject` 

Answer 1

嘗試一下，如果你想要的東西恢復else-

SELECT a.`subject`, GROUP_CONCAT(a.student_id SEPARATOR ',') AS sid, CONCAT(b.fname,' ',b.surname) AS 'name' 
FROM email AS a 
LEFT JOIN student_registration AS b ON b.student_id=a.student_id 
GROUP BY a.`subject`;