题解 | #平均活跃天数和月活人数#

```# count(distinct uid,date(submit_time) 注意 一个人可能存在一天提交2次交券，故去重
select 
    date_format(submit_time,'%Y%m') month,
    round(count(distinct uid,date(submit_time))/ count(distinct uid) ,2) avg_active_days,
    count(distinct uid) nau
from exam_record
where year(submit_time)='2021'
group by month