SELECT up.device_id,
up.university,
SUM(IF(MONTH(date)=8,1,0)) AS question_cnt,
SUM(IF(MONTH(date)=8 AND result='right',1,0)) AS right_question_cnt
FROM user_profile up
LEFT JOIN question_practice_detail qpd
ON up.device_id = qpd.device_id
WHERE university = '复旦大学'
GROUP BY up.device_id
才开始学习mysql 在牛客网上做题 看到的这个解法
为什么select后面可以接没有在group by里出现的字段啊