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');

总结

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