mysql 生成sequence

--生成表语句

CREATE TABLE tb_sequence (
	NAME VARCHAR (50) NOT NULL,
	current_value INT NOT NULL,
	_increment INT NOT NULL DEFAULT 1,
	PRIMARY KEY (NAME)
);
---创建函数
create function _nextval(n varchar(50)) returns integer   
begin  
declare _cur int;  
set _cur=(select current_value from tb_sequence where name= n);  
update tb_sequence  
 set current_value = _cur + _increment  
 where name=n ;  
return _cur;  
end;  
DELIMITER ; 

--插入
insert into tb_sequence values('userid',1000,1); 

--查询结果
select _nextval('userid');