select ifnull(a,'2021汇总'), month_q_cnt, avg_day_q_cnt
from(
select date_format(submit_time,'%Y%m') a, 
count(score) month_q_cnt, 
round(count(score)/MAX(DAY(last_day(submit_time))),3) avg_day_q_cnt
from practice_record
where year(submit_time)=2021
group by a
with rollup) as tb1