题解 | #月总刷题数和日均刷题数#

select submit_month,month_q_cnt,round(month_q_cnt/days,3) month_q_cnt
from(
	select date_format(submit_time,'%Y%m') submit_month,
		count(question_id) month_q_cnt,
		day(date_format(submit_time + interval 1 month,'%Y%m%01')- interval 1 day) days
	from practice_record
	where year(submit_time) = '2021'
	group by date_format(submit_time,'%Y%m'),
		day(date_format(submit_time + interval 1 month,'%Y%m%01')- interval 1 day)
	) as sub
union 
select '2021汇总',
	count(question_id),
	round(count(question_id)/31,3)
from practice_record
where year(submit_time) = '2021'	
order by submit_month;