题解 | #月总刷题数和日均刷题数#

使用union把2021汇总与原表查询汇总到一起,一开始运行老是报错,找了好久才发现分组后没有处理day (last_day (submit_time)),加了个max就显示本月的最大天数了,后面发现没有这个where实例通过不了.
(select
    date_format (submit_time, '%Y%m') submit_month,
    count(1) month_q_cnt,
    ROUND(count(1) / max(day (last_day (submit_time))), 3) avg_day_q_cnt
from
    practice_record
where 
    year(submit_time)=2021
group by
    submit_month)
union
(select
    '2021汇总' as submit_month,
    count(*) submit_month,
    ROUND(count(*) / max(day (last_day (submit_time))), 3) avg_day_q_cnt
from
    practice_record
where 
    year(submit_time)=2021) 
order by 
    submit_month;