题解 | #每天的日活数及新用户占比#

select date(in_time)  as dt ,count(distinct t1.uid) as dau,
round(count(distinct t.uid)/count(distinct t1.uid),2) as uv_new_ratio
from 
    (select uid,in_time from tb_user_log
    union select uid,out_time from tb_user_log)t1 left join 
    (select uid,min(date(in_time)) as dt from tb_user_log group by uid) t 
    on t.uid=t1.uid and t.dt=date(in_time)
group by date(in_time)
order by dt

长期出错的两个点
审题不严
1、活跃没有看到 in_time 和 out time 都算在里面
2、表链接使用了join ，这里肯定是使用left join

这个题并不难，就是爱出小错误。