delete from exam_recordwhere score<60 and TIMESTAMPDIFF(second, start_time, submit_time) < 300

select prod_name,prod_descfrom Productswhere prod_desc like'%toy%'

select  count(distinct device_id) as did_cnt , count(question_id) as question_cntfrom question_practice_detailwhere year(date)=2021 and month(date)=8

select day(date)  as day,count(question_id) as question_cntfrom question_practice_detailwhere month(date)=8 and year(date)=2021group by date 

  我已经通过这道题！ https://www.nowcoder.com/questionTerminal/2d2e37474197488fbdf8f9206f66651c