MySQL序列解决方案_MySQL

MySQL自增长与Oracle序列的区别:
自增长只能用于表中的其中一个字段
自增长只能被分配给固定表的固定的某一字段，不能被多个表共用.
自增长会把一个未指定或NULL值的字段自动填上.
在mysql中添加序列，请看下面的实例：
在MYSQL里有这样一张表:

Java代码

CREATE TABLE Movie(
id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(60) NOT NULL,
released YEAR NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB;

CREATE TABLE Movie(
id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(60) NOT NULL,
released YEAR NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB;

Java代码

INSERT INTO Movie (name,released) VALUES ('Gladiator',2000);
INSERT INTO Movie (id,name,released) VALUES (NULL,'The Bourne Identity',1998);
INSERT INTO Movie (name,released) VALUES ('Gladiator',2000);
INSERT INTO Movie (id,name,released) VALUES (NULL,'The Bourne Identity',1998);

在ORACLE是这样的:

Java代码

CREATE TABLE Movie(
id INT NOT NULL,
name VARCHAR2(60) NOT NULL,
released INT NOT NULL,
PRIMARY KEY (id)
);

CREATE SEQUENCE MovieSeq;

CREATE TABLE Movie(
id INT NOT NULL,
name VARCHAR2(60) NOT NULL,
released INT NOT NULL,
PRIMARY KEY (id)
);

CREATE SEQUENCE MovieSeq;

Java代码

INSERT INTO Movie (id,name,released) VALUES (MovieSeq.NEXTVAL,'Gladiator',2000);
INSERT INTO Movie (id,name,released) VALUES (MovieSeq.NEXTVAL,'Gladiator',2000);

在oracle下为表添加一个触发器，就可以实现mysql自增长功能:

Java代码

CREATE OR REPLACE TRIGGER BRI_MOVIE_TRG
BEFORE INSERT ON Movie
FOR EACH ROW
BEGIN
SELECT MovieSeq.NEXTVAL INTO :new.id FROM DUAL;
END BRI_MOVIE_TRG;
.
RUN;

CREATE OR REPLACE TRIGGER BRI_MOVIE_TRG

BEFORE INSERT ON Movie
FOR EACH ROW
BEGIN
SELECT MovieSeq.NEXTVAL INTO :new.id FROM DUAL;
END BRI_MOVIE_TRG;
.
RUN;

这样，插件记录就可以成为MYSQL风格：

Java代码

INSERT INTO Movie (name,released) VALUES ('The Lion King',1994);
INSERT INTO Movie (name,released) VALUES ('The Lion King',1994);

下面我们来看看如何在mysql数据里使用Oracle序列语法.NEXTVAL 和 .CURVAL.
我们假设在mysql中序列的语法是:

NEXTVAL(’sequence’);
CURRVAL(’sequence’);
SETVAL(’sequence’,value);

下面就是CURRRVAL的实现方案:

Java代码

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;
INSERT INTO sequence VALUES ('MovieSeq',3,5);
DROP FUNCTION IF EXISTS currval;
DELIMITER $
CREATE FUNCTION currval (seq_name VARCHAR(50))
RETURNS INTEGER
CONTAINS SQL
BEGIN
DECLARE value INTEGER;
SET value = 0;
SELECT current_value INTO value
FROM sequence
WHERE name = seq_name;
RETURN value;
END$
DELIMITER ;

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;

INSERT INTO sequence VALUES ('MovieSeq',3,5);
DROP FUNCTION IF EXISTS currval;
DELIMITER $
CREATE FUNCTION currval (seq_name VARCHAR(50))
RETURNS INTEGER
CONTAINS SQL
BEGIN
DECLARE value INTEGER;
SET value = 0;
SELECT current_value INTO value
FROM sequence
WHERE name = seq_name;
RETURN value;
END$
DELIMITER ;

测试一下结果：

Java代码

1. mysql> SELECT currval('MovieSeq');
2. +---------------------+
3. | currval('MovieSeq') |
4. +---------------------+
5. | 3 |
6. +---------------------+
7. 1 row in set (0.00 sec)
8. mysql> SELECT currval('x');
9. +--------------+
10. | currval('x') |
11. +--------------+
12. | 0 |
13. +--------------+
14. 1 row in set, 1 warning (0.00 sec)
15. mysql> show warnings;
16. +---------+------+------------------+
17. | Level | Code | Message |
18. +---------+------+------------------+
19. | Warning | 1329 | No data to FETCH |
20. +---------+------+------------------+
21. 1 row in set (0.00 sec)

mysql> SELECT currval('MovieSeq');

+---------------------+

| currval('MovieSeq') |

+---------------------+

| 3 |

+---------------------+

1 row in set (0.00 sec)

mysql> SELECT currval('x');

+--------------+

| currval('x') |

+--------------+

| 0 |

+--------------+

1 row in set, 1 warning (0.00 sec)

mysql> show warnings;

+---------+------+------------------+

| Level | Code | Message |

+---------+------+------------------+

| Warning | 1329 | No data to FETCH |

+---------+------+------------------+

1 row in set (0.00 sec)

nextval

Java代码

1. DROP FUNCTION IF EXISTS nextval;
2. DELIMITER $
3. CREATE FUNCTION nextval (seq_name VARCHAR(50))
4. RETURNS INTEGER
5. CONTAINS SQL
6. BEGIN
7. UPDATE sequence
8. SET current_value = current_value + increment
9. WHERE name = seq_name;
10. RETURN currval(seq_name);
11. END$
12. DELIMITER ;

Java代码

1. mysql> select nextval('MovieSeq');
2. +---------------------+
3. | nextval('MovieSeq') |
4. +---------------------+
5. | 15 |
6. +---------------------+
7. 1 row in set (0.09 sec)
8.
9. mysql> select nextval('MovieSeq');
10. +---------------------+
11. | nextval('MovieSeq') |
12. +---------------------+
13. | 20 |
14. +---------------------+
15. 1 row in set (0.01 sec)
16.
17. mysql> select nextval('MovieSeq');
18. +---------------------+
19. | nextval('MovieSeq') |
20. +---------------------+
21. | 25 |
22. +---------------------+
23. 1 row in set (0.00 sec)

setval

Java代码

1. DROP FUNCTION IF EXISTS setval;
2. DELIMITER $
3. CREATE FUNCTION setval (seq_name VARCHAR(50), value INTEGER)
4. RETURNS INTEGER
5. CONTAINS SQL
6. BEGIN
7. UPDATE sequence
8. SET current_value = value
9. WHERE name = seq_name;
10. RETURN currval(seq_name);
11. END$
12. DELIMITER ;

Java代码

1. mysql> select setval('MovieSeq',150);
2. +------------------------+
3. | setval('MovieSeq',150) |
4. +------------------------+
5. | 150 |
6. +------------------------+
7. 1 row in set (0.06 sec)
8.
9. mysql> select curval('MovieSeq');
10. +---------------------+
11. | currval('MovieSeq') |
12. +---------------------+
13. | 150 |
14. +---------------------+
15. 1 row in set (0.00 sec)
16.
17. mysql> select nextval('MovieSeq');
18. +---------------------+
19. | nextval('MovieSeq') |
20. +---------------------+
21. | 155 |
22. +---------------------+
23. 1 row in set (0.00 sec)

作者“ERDP技术架构”