题解 | #月总刷题数和日均刷题数#

select ifnull(submit_month,'2021汇总') as submit_month,month_q_cnt,avg_day_q_cnt
from (
select date_format(submit_time,'%Y%m') as submit_month,
count(*) as month_q_cnt,
round(count(*)/day(last_day(min(submit_time))),3) as avg_day_q_cnt
from practice_record
where year(submit_time)=2021
group by submit_month with rollup 
order by grouping(submit_month),submit_month ) a

用好group by col1 with rollup 和grouping(col1)