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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