题解 | #月总刷题数和日均刷题数#

select 
date_format(submit_time,'%Y%m') submit_month,
count(submit_time) month_q_cnt,
round(count(*)/max(day(last_day(submit_time))),3) avg_day_q_cnt
from practice_record
where
year(submit_time)='2021'
group by submit_month
union
select '2021汇总' submit_month,count(*) month_q_cnt,round(count(*)/31,3) avg_day_q_cnt
from practice_record
where 
year(submit_time)='2021'
order by submit_month