select date(in_time) as dt,
round(sum(timestampdiff(second,in_time,out_time))/count( distinct uid),1) as avg_viiew_len_sec
from tb_user_log
where substr(in_time,1,7) ='2021-11' 
and artical_id != 0
group by date(in_time)
order by avg_viiew_len_sec

and artical_id != 0重点是把这句放在where条件里，而非round(sum(timestampdiff(second,in_time,out_time))/count( distinct uid),1) as avg_viiew_len_sec这里