超详细的mysql数据库创建自增序列实现过程

158人浏览 2023-10-23 14:26:41

概述

由于mysql和oracle不太一样，不支持直接的sequence，所以需要创建一张table来模拟sequence的功能。

1、创建sequence表

CREATE TABLE `sequence` (
	`name` VARCHAR ( 50 ) COLLATE utf8_bin NOT NULL COMMENT '序列的名字',
	`current_value` INT ( 11 ) NOT NULL COMMENT '序列的当前值',
	`increment` INT ( 11 ) NOT NULL DEFAULT '1' COMMENT '序列的自增值',
PRIMARY KEY ( `name` ) 
) ENGINE = INNODB DEFAULT CHARSET = utf8 COLLATE = utf8_bin;

2、创建–取当前值的函数

DROP FUNCTION IF EXISTS currval; 
DELIMITER $ 
CREATE FUNCTION currval (seq_name VARCHAR(50)) 
 RETURNS INTEGER 
 LANGUAGE SQL 
 DETERMINISTIC 
 CONTAINS SQL 
 SQL SECURITY DEFINER 
 COMMENT '' 
BEGIN 
 DECLARE value INTEGER; 
 SET value = 0; 
 SELECT current_value INTO value 
 FROM sequence 
 WHERE name = seq_name; 
 RETURN value; 
END
$ 
DELIMITER ;

3、创建–取下一个值的函数

DROP FUNCTION IF EXISTS nextval; 
DELIMITER $ 
CREATE FUNCTION nextval (seq_name VARCHAR(50)) 
 RETURNS INTEGER 
 LANGUAGE SQL 
 DETERMINISTIC 
 CONTAINS SQL 
 SQL SECURITY DEFINER 
 COMMENT '' 
BEGIN 
 UPDATE sequence 
 SET current_value = current_value + increment 
 WHERE name = seq_name; 
 RETURN currval(seq_name); 
END 
$ 
DELIMITER ;

4、创建–更新当前值的函数

DROP FUNCTION IF EXISTS setval; 
DELIMITER $ 
CREATE FUNCTION setval (seq_name VARCHAR(50), value INTEGER) 
 RETURNS INTEGER 
 LANGUAGE SQL 
 DETERMINISTIC 
 CONTAINS SQL 
 SQL SECURITY DEFINER 
 COMMENT '' 
BEGIN 
 UPDATE sequence 
 SET current_value = value 
 WHERE name = seq_name; 
 RETURN currval(seq_name); 
END 
$ 
DELIMITER ;

5、测试

INSERT INTO sequence VALUES ('hwb_Seq', 0, 1);--添加一个sequence名称和初始值，以及自增幅度
SELECT SETVAL('hwb_Seq', 10);--设置指定sequence的初始值
SELECT CURRVAL('hwb_Seq');--查询指定sequence的当前值
SELECT NEXTVAL('hwb_Seq');--查询指定sequence的下一个值