MySQL如何生成自增的流水号

select concat('A', 'B', 'C');

select now();

select date_format(now() , '%Y%m%d');

select lpad('A' , 4 , 0);

select concat('SP',date_format(now(),'%Y%m%d') , lpad('1' , 4 , 0));

select concat('SP',date_format(now(),'%Y%m%d') , lpad(max(right(shoppingNum , 4)) + 1 , 4 , 0)) from mytest m 

insert  into mytest values(3,now(), (select concat('SP',date_format(now(),'%Y%m%d') , lpad(max(right(shoppingNum , 4)) + 1 , 4 , 0)) from mytest ));

CREATE TABLE orders (
	sn_day DECIMAL (32) PRIMARY KEY,
	sn_hours DECIMAL (32),
	sn_minutes DECIMAL (32),
	remark VARCHAR (100)
);

CREATE TRIGGER sn_by_day BEFORE INSERT ON orders FOR EACH ROW
BEGIN
	DECLARE
		n INT;
SELECT
	IFNULL(max(RIGHT(sn_day, 10)), 0) INTO n
FROM
	orders
WHERE
	mid(sn_day, 1, 8) = DATE_FORMAT(NOW(), '%Y%m%d');
SET NEW.sn_day = concat(
	DATE_FORMAT(NOW(), '%Y%m%d'),
	RIGHT (10000000001 + n, 10)
);
END;

#强势插入一条数据,看能不能自动生成序列号
INSERT orders (remark) VALUES (CONCAT('demo',DATE_FORMAT(NOW(),'%Y-%m-%d %h:%i:%s')));

CREATE TRIGGER sn_by_hours BEFORE INSERT ON orders FOR EACH ROW
BEGIN
	DECLARE
		n INT;
SELECT
	IFNULL(max(RIGHT(sn_hours, 8)), 0) INTO n
FROM
	orders
WHERE
	mid(sn_hours, 1, 10) = FROM_UNIXTIME(
		UNIX_TIMESTAMP(NOW(6)),
		'%Y%m%d%h'
	);
SET NEW.sn_hours = concat(
	FROM_UNIXTIME(
		UNIX_TIMESTAMP(NOW(6)),
		'%Y%m%d%h'
	),
	RIGHT (100000001 + n, 8)
);
END;

CREATE TRIGGER sn_by_minutes BEFORE INSERT ON orders FOR EACH ROW
BEGIN
	DECLARE
		n INT;
SELECT
	IFNULL(max(RIGHT(sn_minutes, 6)), 0) INTO n
FROM
	orders
WHERE
	mid(sn_minutes, 1, 12) = FROM_UNIXTIME(
		UNIX_TIMESTAMP(NOW(6)),
		'%Y%m%d%h%i'
	);
SET NEW.sn_minutes = concat(
	FROM_UNIXTIME(
		UNIX_TIMESTAMP(NOW(6)),
		'%Y%m%d%h%i'
	),
	RIGHT (1000001 + n, 6)
);
END;