mysql code to implement sequence function

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;

DELIMITER $$
CREATE DEFINER=`root`@`%` FUNCTION `_nextval`(name varchar(50)) RETURNS int(11)
begin 
declare _cur int;
declare _maxvalue int; -- receive the maximum value declare _increment int; -- receive the number of increment steps set _increment = (select increment_value from sys_sequence where seq_name = name);
set _maxvalue = (select max_value from sys_sequence where seq_name = name);
set _cur = (select current_value from sys_sequence where seq_name = name); 
update sys_sequence -- Update the current value set current_value = _cur + increment_value 
where seq_name = name ; 
if(_cur + _increment >= _maxvalue) then -- Check if both have reached the maximum value update sys_sequence 
    set current_value = min_value 
    where seq_name = name ;
end if;
return _cur; 
end$$
DELIMITER ;

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

select _nextval('seq_name1');