ORACLE自动递增--序列

关于oracle的自动递增，一般依靠序列来产生。当然没SQL SERVICE 2005那样两粒简单的关键字就吃定。
创建序列的语法：
CREATE SEQUENCE 序列名
[INCREMENT BY n]  --增长量，默认为1，负值为减量
[START WITH n]  ---初始值 ，默认为1
[{MAXVALUE/ MINVALUE n|NOMAXVALUE}]--最大值，最小值，默认不规定最大最小值
[{CYCLE|NOCYCLE}]--达到最大值循环或不循环
[{CACHE n|NOCACHE}]; --缓冲，爱理不理的。

个人认为以下三个选项少用 :

[{MAXVALUE/ MINVALUE n|NOMAXVALUE}]

[{CYCLE|NOCYCLE}]

[{CACHE n|NOCACHE}];

不管你信不信，反正我信了，我就是没曾用过。

创建一张测试表：

 

SQL> create table testseq(
  2  next number,
  3  curr number
  4  );

Table created

（1）最常用的，最简单的序列：

 

SQL> create sequence myseq;

Sequence created

   插入五条数据测试：

 

SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted

SQL> select * from testseq;

      NEXT       CURR
---------- ----------
         1          1
         2          2
         3          3
         4          4
         5          5

（2）改变增量的序列

 

SQL> drop sequence myseq;

Sequence dropped
SQL> delete from testseq;

5 rows deleted

SQL> create sequence myseq increment by 10;

Sequence created

 插入五条数据测试：

 

SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted

SQL> select * from testseq;

      NEXT       CURR
---------- ----------
         1          1
        11         11
        21         21
        31         31
        41         41

（3）设置初始值的序列

 

SQL> drop sequence myseq;

Sequence dropped

SQL> delete from testseq;

5 rows deleted

SQL> create sequence myseq increment by 10 start with 25;

Sequence created

 插入五条数据测试：

 

SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted

SQL> select * from testseq;

      NEXT       CURR
---------- ----------
        25         25
        35         35
        45         45
        55         55
        65         65

SQL>

（4）设置序列的最大值-----挺少用，十分少用

 

SQL> drop sequence myseq;

Sequence dropped
SQL> delete from testseq;

5 rows deleted

SQL> create sequence myseq increment by 10 start with 25 maxvalue 50;

Sequence created

SQL>
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

1 row inserted
SQL> insert into testseq values(myseq.nextval,myseq.currval);

insert into testseq values(myseq.nextval,myseq.currval)

ORA-08004: 序列 MYSEQ.NEXTVAL exceeds MAXVALUE 无法实例化
SQL> insert into testseq values(myseq.nextval,myseq.currval);

insert into testseq values(myseq.nextval,myseq.currval)

ORA-08004: 序列 MYSEQ.NEXTVAL exceeds MAXVALUE 无法实例化
 c
SQL> select * from testseq;

      NEXT       CURR
---------- ----------
        25         25
        35         35
        45         45

SQL>

你可以看出，当插入数据超过最大值的时候，就会产生错误。况且平常这种操作几乎没用，最大值设置感觉没意义。

掌握前面三个常用的序列方法就够应付平常的序列问题了。