题解 | #月总刷题数和日均刷题数#

SELECT
    DATE_FORMAT(submit_time,"%Y%m") submit_month,
    COUNT(submit_time) month_q_cnt,
    round(COUNT(submit_time) / MAX(DAY(last_day(submit_time))),3)avg_day_q_cnt
FROM
    practice_record
WHERE
    year(submit_time) = '2021'
GROUP BY
    DATE_FORMAT(submit_time,"%Y%m") 

union all

SELECT '2021汇总' submit_month,count(submit_time) month_q_cnt,round(count(submit_time) /31 ,3)avg_day_q_cnt
FROM
    practice_record
WHERE
    year(submit_time) = '2021' 

ORDER BY submit_month

union all 在最后一行结果拼接，列名要相同

简洁函数报错：

函数：

with rollup ：将分组后的结果进行加和

coalesce(expression,1) 如果表达式为null返回1