题解 | #各个视频的平均完播率#
平均活跃天数和月活人数
http://www.nowcoder.com/practice/9e2fb674b58b4f60ac765b7a37dde1b9
select mon,round(sum(num)/count(distinct uid),2),count(distinct uid) from (select date_format(start_time,'%Y%m') mon,uid ,count(distinct date_format(start_time,'%Y%m%dd')) num from exam_record where score is not null and year(start_time)='2021' group by mon,uid)a group by mon
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