/* 需求：计算2021年试卷作答区 用户平均活跃天数，结果两位小数 问题分解 1.2021 where 限定条件 date_format(subMit_time)=2021 2.avg_active_days=总用户月总活跃天数/用户数(count(distinct)) 3.mau 月度活跃人数=count(distinct uid) 4.group by month(date_format(submit_time,"%Y%m")) */ select date_format(submit_time,'%Y%m'), round((count(distinct uid,DATE_FORMAT(submit_time,'%Y%m%d')))/ count(distinct uid),2), count(distinct uid) from exam_record where year(submit_time)=2021 and submit_time is not NULL group by date_format(submit_time,'%Y%m')