1.将序列号作为分组查询的条件，在将查询出来的结果进行筛选。
select t.serial_number,count(t.serial_number) from stamp_info t group by t.serial_number
select t.serial_number,count(t.serial_number) from stamp_info t group by t.serial_number having count(t.serial_number) > 1;
原文：https://www.cnblogs.com/HeiDi-BoKe/p/11760474.html