请问在造表的时候分组，会报错是什么原因呀，如果在造表的时候分组一次，外头筛选的时候也分组一次，报错是什么原因呢 select uid, round(avg(new_score),0)as avg_score, round(avg(cost_time),1)as avg_time_took from(select e_r.uid as uid, if(score is null,0,score) as new_score, if(submit_time is null,duration,timestampdiff(minute,start_time,submit_time)) as cost_time from exam_record e_r left join examination_info e_i on e_i.exam_id=e_r.exam_id left join user_info u_i on u_i.uid=e_r.uid where level =0 and difficulty = 'hard' # group by uid ) new_table group by uid