mysql 自增序列

1:原理是在建立一个触发器TRIGGER tri_NewBH  在table插入时执行序列计算

 

mysql> CREATE TABLE tb(BH CHAR(16),content VARCHAR(20),`date` DATETIME,val INT);

Query OK, 0 rows affected (0.05 sec)



mysql>

mysql>

mysql> DELIMITER $$

mysql> DROP TRIGGER IF EXISTS tri_NewBH $$

Query OK, 0 rows affected, 1 warning (0.00 sec)



mysql>

mysql> CREATE TRIGGER tri_NewBH BEFORE INSERT ON tb

    -> FOR EACH ROW

    -> BEGIN

    ->     DECLARE dt CHAR(8);

    ->     DECLARE bh_id CHAR(16);

    ->     DECLARE number INT;

    ->     DECLARE new_bh VARCHAR(16);

    ->

    ->     SET dt = DATE_FORMAT(CURDATE(),'%Y%m%d');

    ->

    ->     SELECT

    ->         MAX(BH) INTO bh_id

    ->     FROM tb

    ->     WHERE BH LIKE CONCAT(dt,'%');

    ->

    ->     IF bh_id = '' OR bh_id IS NULL THEN

    ->         SET new_bh = CONCAT(dt,'00000001');

    ->     ELSE

    ->         SET number = RIGHT(bh_id,8) + 1;

    ->         SET new_bh =  RIGHT(CONCAT('00000000',number),8);

    ->         SET new_bh=CONCAT(dt,new_bh);

    ->     END IF;

    ->

    ->     SET NEW.BH = new_bh;

    -> END$$

Query OK, 0 rows affected (0.09 sec)



mysql>

mysql> DELIMITER ;

mysql> INSERT INTO tb(content,`date`,val) VALUES('LiangCK','2009-05-11',20);

Query OK, 1 row affected (0.00 sec)



mysql> INSERT INTO tb(content,`date`,val) VALUES('LiangCK','2009-05-11',20);

Query OK, 1 row affected (0.01 sec)



mysql> INSERT INTO tb(content,`date`,val) VALUES('LiangCK','2009-05-11',20);

Query OK, 1 row affected (0.00 sec)



mysql> INSERT INTO tb(content,`date`,val) VALUES('LiangCK','2009-05-11',20);

Query OK, 1 row affected (0.00 sec)



mysql> INSERT INTO tb(content,`date`,val) VALUES('LiangCK','2009-05-11',20);

Query OK, 1 row affected (0.00 sec)



mysql> INSERT INTO tb(content,`date`,val) VALUES('LiangCK','2009-05-11',20);

Query OK, 1 row affected (0.01 sec)



mysql> INSERT INTO tb(content,`date`,val) VALUES('LiangCK','2009-05-11',20);

Query OK, 1 row affected (0.00 sec)



mysql> SELECT * FROM tb;

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

| BH               | content | date                | val  |

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

| 2009051100000001 | LiangCK | 2009-05-11 00:00:00 |   20 |

| 2009051100000002 | LiangCK | 2009-05-11 00:00:00 |   20 |

| 2009051100000003 | LiangCK | 2009-05-11 00:00:00 |   20 |

| 2009051100000004 | LiangCK | 2009-05-11 00:00:00 |   20 |

| 2011051200000001 | LiangCK | 2009-05-11 00:00:00 |   20 |

| 2011051200000002 | LiangCK | 2009-05-11 00:00:00 |   20 |

| 2011051200000003 | LiangCK | 2009-05-11 00:00:00 |   20 |

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

7 rows in set (0.00 sec)

 

2.下面就是另外一个的实现方案: 

原理是创建一个专门记录序列的表sequence,记录有当前序列号,序列的间隔如+1

 

DROP TABLE IF EXISTS sequence;/*创建记录当前序列的表*/

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 $/*创建一个获取当前序列的function*/

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：

 

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 

 

//获取下一个数值..先在 sequence里面调用update当前最大数值+1然后再调用 currval获得当前数值

 

DROP FUNCTION IF EXISTS nextval;

DELIMITER $

CREATE FUNCTION nextval (seq_name VARCHAR(50))

RETURNS INTEGER

CONTAINS SQL

BEGIN

   UPDATE sequence

   SET          current_value = current_value + increment

   WHERE name = seq_name;

   RETURN currval(seq_name);

END$

DELIMITER ;

 

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

| nextval('MovieSeq') |

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

|                  15 |

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

1 row in set (0.09 sec)



mysql> select nextval('MovieSeq');

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

| nextval('MovieSeq') |

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

|                  20 |

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

1 row in set (0.01 sec)



mysql> select nextval('MovieSeq');

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

| nextval('MovieSeq') |

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

|                  25 |

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

1 row in set (0.00 sec)

setval

 

DROP FUNCTION IF EXISTS setval;

DELIMITER $

CREATE FUNCTION setval (seq_name VARCHAR(50), value INTEGER)

RETURNS INTEGER

CONTAINS SQL

BEGIN

   UPDATE sequence

   SET          current_value = value

   WHERE name = seq_name;

   RETURN currval(seq_name);

END$

DELIMITER ;

 

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

| setval('MovieSeq',150) |

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

|                    150 |

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

1 row in set (0.06 sec)



mysql> select curval('MovieSeq');

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

| currval('MovieSeq') |

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

|                 150 |

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

1 row in set (0.00 sec)



mysql> select nextval('MovieSeq');

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

| nextval('MovieSeq') |

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

|                 155 |

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

1 row in set (0.00 sec)