select device_id,university, count(question_id) as question_cnt, sum(distinct if(result='right',1,0)) right_question_cnt from (select university,device_id from user_profile where university='复旦大学') as a left join (select * from question_practice_detail where month(date) =8) AS b using (device_id) group by device_id, university;本地试了完全没问题,在线运行就是错的,啥情况