题解 | #删除记录（二）#

delete from exam_record
where submit_time is null or timestampdiff(minute,start_time,submit_time)<5 
order by start_time limit 3

问题分解：

1. 未完成作答，即subtmit_time is null, 作答时间小于5分钟整，即：timestampdiff(minute,start_time,submit_time) <5

2. 开始作答时间最早的3条记录，取前三条，按start_time排序，order by start_time limit 3

3. 删除语句delete from exam_record where...