题解 | #21年8月份练题总数# 三种限定时间条件的方法

正确题解：

select count(distinct device_id) as did_cnt,
count(question_id) as question_cnt
from question_practice_detail
where year(date)=2021 and month(date)=8

刚学完year和month函数，所以这道题一次就通过了，但还有两种限定时间条件的方法，需要掌握！

个人感觉year、month函数和like语法比较好理解，date_format函数格式有些复杂

限定条件：2021年8月份，匹配date字段即可，匹配方法主要有三种：

（1）like语法：date like "2021-08%"

（2）year、month函数：year(date)='2021' and month(date)='08'

（3）date_format函数：date_format(date, '%Y-%m')='2021-08'

另两种方法：

elect count(distinct device_id) as did_cnt,
count(question_id) as question_cnt
from question_practice_detail
where date like '2021-08%'

select count(distinct device_id) as did_cnt,
count(question_id) as question_cnt
from question_practice_detail
where date_format(date, '%Y-%m') = '2021-08'