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 date like ('2021-08%')
#重点是where句，他有三种改法
#1.like写法：where date like ('2021-08%)
#2.正则表达式写法：where date regexp '2021-08'
#3.substring写法：where substring(date,1,7) = '2021-08' 即date字符串第一个到第七个截取的子串为‘2021-08’
group by date;