题解 | #21年8月份练题总数#

select 
     count(distinct device_id) as did_cnt,
     count(question_id) as question_cut
from question_practice_detail

where date like '2021-08%'

group by添加在聚合函数后面，日期还可以用like‘’表示。只写了月份要08，怪不得答案不对哈哈哈哈哈