delete from exam_record
where submit_time is null
#sql中使用timestampdiff函数获取时间差
or timestampdiff(minute,start_time,submit_time)<5
order by start_time
limit 3;
delete from exam_record
where submit_time is null
#sql中使用timestampdiff函数获取时间差
or timestampdiff(minute,start_time,submit_time)<5
order by start_time
limit 3;