题解 | #月总刷题数和日均刷题数#

select coalesce(year_mon,'2021汇总') as submit_month,
count(question_id) as month_q_cnt,
round(count(question_id)/max(t.days_month),3) as avg_day_cnt
from
(select question_id,
dayofmonth(last_day(submit_time)) as days_month,
date_format(submit_time,'%Y%m') as year_mon
from practice_record
where year(submit_time)=2021) as t
group by t.year_mon
with rollup;

我真的不明白，高赞的思路复制粘贴上去都是错的，是它出bug吗？这个答案也和我自己写的几乎一样，但是就报错，显示不出2021汇总，明明都是coalesce函数，真的搞不明白，头痛