delete from exam_record where submit_time is null or timestampdiff(minute,start_time ,submit_time)<5 order by start_time asc limit 3 #delete 本质就是把按条件查找到的语句删了，所以不需要在delete 后面＋个select 语句了 #limit的用法 limit x,y 跳过x取y 条数据