根据需求，保存表数据时需要自动生成一个编号，格式如：AA-2020-03-31-0001 （AA-yyyy-MM-dd-序号）。数据库用的mysql，所以创建一个mysql函数。
1、建表：
create table sys_sequence_number(
sequenceType varchar(30) not null,
val int not null,
len int not null
);
2、建函数
DELIMITER $$
DROP FUNCTION IF EXISTS getSequenceNo $$
create function getSequenceNo(pSequenceType varchar(30),pLen int) returns varchar(60)
begin
declare strZero varchar(20) default '00000000000000000000';
declare strSequenceNo varchar(60) default '';
declare iVal int default 0;
declare iLen int default 0;
declare c int default 0;
select count(1) into c from sys_sequence_number where sequenceType=pSequenceType;
if(c<1)
then
insert into sys_sequence_number(sequenceType,val,len)
values(pSequenceType,0,pLen);
end if;
update sys_sequence_number set val=val+1 where sequenceType=pSequenceType;
select val,len into iVal,iLen from sys_sequence_number where sequenceType=pSequenceType;
set strSequenceNo=concat(substr(strZero,1,iLen-length(iVal)),convert(iVal,char(10)));
return concat(concat(pSequenceType,'-'),strSequenceNo);
end $$
DELIMITER ;
3、在mysql上执行测试： select getSequenceNo(concat('AA-',date_format(now(), '%Y-%m-%d')),4)