题解 | #得分不小于平均分的最低分#
平均活跃天数和月活人数
http://www.nowcoder.com/practice/9e2fb674b58b4f60ac765b7a37dde1b9
select date_format(start_time,'%Y%m') month , round(COUNT(DISTINCT uid,DATE_FORMAT(start_time,'%Y%m%d')) /count(DISTINCT uid) ,2) avg_active_days, COUNT(DISTINCT(uid))
from exam_record where year(submit_time)=2021 group by month