题解 | #分组过滤练习题#
平均活跃天数和月活人数
http://www.nowcoder.com/practice/9e2fb674b58b4f60ac765b7a37dde1b9
select replace(SUBSTRING(start_time,1,7),"-",""), round(count(distinct uid, date_format(submit_time, '%Y%m%d')) / count(distinct uid),2), count(distinct uid) from exam_record where not ISNULL(submit_time) and date_format(submit_time,'%y') = '21' group by substring(start_time,1,7)