题解 | #月总刷题数和日均刷题数#

select extract(year_month from  submit_time) submit_month, 
    count(*) month_q_cnt,
    round(count(*)/avg(day(last_day(submit_time))),3) avg_day_q_cnt
from practice_record
where year(submit_time) = '2021'
group by extract(year_month from submit_time) 
union
select '2021汇总' as 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;