题解 | #平均活跃天数和月活人数#

select date_format(submit_time,'%Y%m') as 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 start_time like'2021%' and submit_time is not null
group by date_format(submit_time,'%Y%m');

最大的收获，原来count()函数里面可以有不止一列。。。