【MySQL】實現自增函數sequence

前言

當前數據庫為：mysql
由於mysql和oracle不太一樣，不支持直接的sequence，所以需要創建一張table來模擬sequence的功能，理由sql語句如下：

步驟

1.創建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 '序列的當前值',
  `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.創建取當前值的函數

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.創建取下一個值函數

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.創建更新當前值函數

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 ; 

數據庫結構

 

 調用

INSERT INTO sequence VALUES ('testSeq', 0, 1);--添加一個sequence名稱和初始值，以及自增幅度

SELECT SETVAL('testSeq', 10);--設置指定sequence的初始值

SELECT CURRVAL('testSeq');--查詢指定sequence的當前值

SELECT NEXTVAL('testSeq');--查詢指定sequence的下一個值