select DISTINCT date_format(start_time,'%Y%m') month, round(count(distinct uid,date_format(submit_time,'%y%m%d'))/count(distinct uid),2) as avg_active_days, COUNT(DISTINCT uid) AS mau FROM exam_record where YEAR(start_time)='2021' and submit_time is not null GROUP BY month ; 1.这里先是有一个按照时间分组的:GROUP B...