mysql实现sequence功能的代码

mysql实现sequence功能

1.建立sequence记录表

CREATE TABLE `sys_sequence` (
`seq_name` varchar(50) CHARACTER SET latin1 COLLATE latin1_bin NOT NULL,
`min_value` int(11) NOT NULL,
`max_value` int(11) NOT NULL,
`current_value` int(11) NOT NULL,
`increment_value` int(11) NOT NULL DEFAULT '1',
PRIMARY KEY (`seq_name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

 2.建立sequence基础函数

DELIMITER $$
CREATE DEFINER=`root`@`％` FUNCTION `_nextval`(name varchar(50)) RETURNS int(11)
begin
declare _cur int;
declare _maxvalue int; -- 接收最大值
declare _increment int; -- 接收增长步数
set _increment = (select increment_value from sys_sequence where seq_name = name);
set _maxvalue = (select max_value from sys_sequence where seq_name = name);
set _cur = (select current_value from sys_sequence where seq_name = name);
update sys_sequence           -- 更新当前值
set current_value = _cur + increment_value
where seq_name = name ;
if(_cur + _increment >= _maxvalue) then -- 判断是都达到最大值
  update sys_sequence
   set current_value = min_value
   where seq_name = name ;
end if;
return _cur;
end$$
DELIMITER ;

3.插入想要建立的sequence

INSERT INTO `mydb`.`sys_sequence`
(`seq_name`,
`min_value`,
`max_value`,
`current_value`,
`increment_value`)
VALUES
('seq_name1', 1, 99999999, 1, 1);

4.使用sequence

select _nextval('seq_name1');

来源：https://blog.csdn.net/laladebon/article/details/82256194