题解 | #21年8月份练题总数#

select count(DISTINCT device_id) as did_cnt,count(question_id) as question_cnt from question_practice_detail where date>='2021-08-01' and date <='2021-08-31';
从question_practice_detail表中 计算用户总数(可能有重复的) as做为别名did_cnt  
count(question_id)总数 as 作为别名question_cnt  
where条件判定 'date>='2021-08-01' and 'date <='2021-08-31';