题解 | #月总刷题数和日均刷题数#

第三种方法

select date_format(submit_time,'%Y%m') submit_month,
count(question_id) month_q_cnt,
round(count(question_id)/ AVG(day(LAST_DAY(submit_time))),3) avg_day_q_cnt
from practice_record
where date_format(submit_time,'%Y')='2021'
group by submit_month
union all
select '2021汇总' as submit_month,
count(question_id) month_q_cnt,
round(count(id)/31,3) avg_day_q_cnt
from practice_record
where date_format(submit_time,'%Y')='2021'
order by submit_month;