/**
用substr 截取字符串,
substr(string,start,length)
注意:mysql中的start是从1开始的。
**/
select substr(date,9,2)as day,count(question_id) as question_cnt from question_practice_detail where substr(date,1,7)='2021-08' group by day;
select substr(date,9,2)as day,count(question_id) as question_cnt from question_practice_detail where substr(date,1,7)='2021-08' group by day;