题解 | #月总刷题数和日均刷题数#
月总刷题数和日均刷题数
https://www.nowcoder.com/practice/f6b4770f453d4163acc419e3d19e6746
select coalesce(submit_month,'2021汇总') as submit_month, count(submit_time) as month_q_cnt, round(count(submit_time)/ MAX(DAY(last_day(submit_time))),3)as avg_day_q_cnt from ( select *,date_format(submit_time,'%Y%m') as submit_month from practice_record)t where year(submit_time)='2021' group by submit_month with rollup
直接coalesce不行，需要再套一层，不清楚为什么，有朋友知道缘由嘛
