mysql實現sequence功能

 mysql實現sequence功能
 
 1.建立sequence記錄表

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基礎函數

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; -- 接收增長步數
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                      -- 更新當前值
set current_value = _cur + increment_value  
where seq_name = name ;  
if(_cur + _increment >= _maxvalue) then  -- 判斷是都達到最大值
     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');