select date_format(submit_time,'%Y%m') as month,
round((count(distinct uid, date_format(submit_time,'%Y%m%d')))/count(distinct uid),2) avg_active_days,
count(distinct uid) mau
from exam_record
where year(submit_time)=2021 and submit_time is not null
group by date_format(submit_time,'%Y%m')