题解 | 21年8月份练题总数

解析：1.时间函数的操作： 2021 year(date) = 2021
月份 8 month(date) = 8 
2.统计总用户数
需要对device_id 进行去重 然后进行一个count聚合函数的统计
select count(distinct device_id) as did_cnt,
count(*) as question_cnt
from question_practice_detail
where year(date) = 2021 and month(date) = 8;