引用
由于mysq只有递增列的概念没有oracle的sequence功能,这样对于以前习惯用oracle数据库开发的程序员不太实用,尤其在要使用nextval在获取增长序列的时候。这样就设计一个能模拟oracle sequence的功能。
思路:我们可以用一张表来记录sequence数据,其实在使用oracle sequence的时候也类似是一张表,currentval、nextval和增长系数就类似表中的字段。而currentval、nextval我们可以设计成两个function这样在调用的时候返回currentval、nextval的值。
设计表seqMsql:
[sql] view plain copy
CREATE TABLE seqMysql
(
seqname VARCHAR(50) NOT NULL, --sequence名称
currentValue INT NOT NULL, --当前sequence值
increment INT NOT NULL DEFAULT 1, --增长系数
PRIMARY KEY (seqname)
) ENGINE=InnoDB;
实例:插入一个sequence数据
[sql] view plain copy
INSERT INTO seqMysql VALUES ('browserSeq',10002,1);
查询:
[sql] view plain copy
+------------+--------------+-----------+
| seqname | currentValue | increment |
+------------+--------------+-----------+
| browserSeq | 10002 | 1 |
+------------+--------------+-----------+
1 row in set
获取当前值function:
[sql] view plain copy
DELIMITER $
CREATE FUNCTION currval (seq_name VARCHAR(50))
RETURNS INTEGER
CONTAINS SQL
BEGIN
DECLARE current INTEGER;
SET current = 0;
SELECT currentValue INTO current
FROM seqMysql
WHERE seqname = seq_name;
RETURN current;
END$
DELIMITER ;
查询:
[sql] view plain copy
mysql> SELECT currval('browserSeq');
+--------------------+
| currval('browserSeq')|
+--------------------+
| 10002 |
+--------------------+
1 row in set
获取下一个值function:
[sql] view plain copy
DELIMITER $
CREATE FUNCTION nextval (seq_name VARCHAR(50))
RETURNS INTEGER
CONTAINS SQL
BEGIN
UPDATE seqMysql
SET currentValue = currentValue + increment
WHERE seqname = seq_name;
RETURN currval(seq_name);
END$
DELIMITER ;
查询:
[sql] view plain copy
mysql> SELECT nextval('browserSeq');
+-----------------------+
| nextval('browserSeq') |
+-----------------------+
| 10003 |
+-----------------------+
1 row in set
设置增长系数function:
[sql] view plain copy
DELIMITER $
CREATE FUNCTION setval (seq_name VARCHAR(50), value INTEGER)
RETURNS INTEGER
CONTAINS SQL
BEGIN
UPDATE seqMysql
SET currentValue = value
WHERE seqname = seq_name;
RETURN currval(seq_name);
END$
DELIMITER ;