题解 | #计算用户8月每天的练题数量#

select day(date) as day, count(question_id) as question_cnt
from question_practice_detail
where year(date) = '2021' and month(date) = '8'
group by date;

tmd,注意分组，说的是每天的，有聚合函数的时候一定要注意要不要分组！！！