select
date(in_time) dt,
round(sum(timestampdiff(second, in_time, out_time))/count(distinct uid),1) avg_view_len_sec
from tb_user_log
where date_format(in_time,'%Y-%m')='2021-11' and artical_id!=0
group by date(in_time)
order by round(sum(timestampdiff(second, in_time, out_time))/count(distinct uid),1)
易错点:
- 按照题目提示计算均值不要用avg啊啊啊啊啊,分子并没有管一个人是不是看了两次,但分母每个人只算一次;
- 注意看背景!背景!背景!筛选条件里很容易忽略比如本题的artical_id
- 记住排序,以后就每个关键字都脑子里过一遍看看是不是有忽略掉的要求!