＃1247 - 参考＆＃39; sid＆＃39;不支持（参考组功能）

Question

（参考群体功能） -

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

尝试一下，如果你想要别的东西还原它 -

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`;