题解 | #平均活跃天数和月活人数#

# 请计算2021年每个月里试卷作答区用户平均月活跃天数
# avg_active_days和月度活跃人数mau，上面数据的示例输出如下：
# 2021年、每个月group by 、平均月活跃天数、月度活跃人数

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