题解 | #月总刷题数和日均刷题数#

select ym submit_month,count(*) month_q_cnt,
round(count(*)/avg(ld),3) avg_day_q_cnt
from (
    select *,extract(year_month from submit_time) ym,
    day(last_day(submit_time)) ld
    from practice_record
    where year(submit_time) = 2021
) t
group by ym

union all

select '2021汇总',count(*),round(count(*)/31,3)
from practice_record
where year(submit_time) = 2021

order by submit_month