题解 | #月总刷题数和日均刷题数#

SELECT submit_month,montn_q_cnt,round(montn_q_cnt/days,3) FROM
(
        SELECT
            ifnull(submit_month,'2021汇总') AS submit_month,
            montn_q_cnt,
            day(last_day(if(submit_month IS NULL ,str_to_date('20210131','%Y%m%d'),concat(submit_month,'01')))) days
        FROM
        (
            SELECT
                date_format(submit_time,'%Y%m') as submit_month,
                count(1) montn_q_cnt
            FROM practice_record
            WHERE year(submit_time) = '2021'
            GROUP BY date_format(submit_time,'%Y%m')
            WITH ROLLUP
        )t1
    )t2
ORDER BY submit_month;

麻瓜思路