select date_format(submit_time,'%Y%m') month,round(count(distinct uid,date_format(submit_time,'%y%m%d'))/count(distinct uid),2) avg_active_days,round(count(distinct uid),2) mau from exam_record where year(start_time)=2021 and submit_time is not null group by month; 1、错误解法:select date_format(submit_t...