自己實現(xiàn)mysql的sequence

明神月 2019-05-05

展開全文

摘自：https://www.runoob.com/mysql/mysql-using-sequences.html

第一步：創(chuàng)建Sequence管理表 sequence

DROP TABLE IF EXISTS sequence; CREATE TABLE sequence ( name VARCHAR(50) NOT NULL, current_value INT NOT NULL, increment INT NOT NULL DEFAULT 1, PRIMARY KEY (name) ) ENGINE=InnoDB;

第二步：創(chuàng)建取當前值的函數(shù) currval

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

第三步：創(chuàng)建取下一個值的函數(shù) nextval

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

第四步：創(chuàng)建更新當前值的函數(shù) setval

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 ''BEGINUPDATE sequence
SET current_value = value 
WHERE name = seq_name; RETURN currval(seq_name); END$ 
DELIMITER ;

測試函數(shù)功能

當上述四步完成后，可以用以下數(shù)據(jù)設(shè)置需要創(chuàng)建的sequence名稱以及設(shè)置初始值和獲取當前值和下一個值。

INSERT INTO sequence VALUES ('TestSeq', 0, 1);----添加一個sequence名稱和初始值，以及自增幅度  添加一個名為TestSeq 的自增序列SELECT SETVAL('TestSeq', 10);---設(shè)置指定sequence的初始值    這里設(shè)置TestSeq 的初始值為10SELECT CURRVAL('TestSeq');  --查詢指定sequence的當前值   這里是獲取TestSeq當前值SELECT NEXTVAL('TestSeq');  --查詢指定sequence的下一個值  這里是獲取TestSeq下一個值