select date_format(in_time,'%Y-%m-%d') as dt ,
round(sum(timestampdiff(second,in_time,out_time))/count(distinct uid),1) as avg_viiew_len_sec
from tb_user_log#求平均值要注意ID要去重
where artical_id!=0 #这里要注意排除掉artical_id为0的
and year(in_time)=2021
and month(in_time)=11
group by dt
order by avg_viiew_len_sec