[CACHE integer | NOCACHE] --指定数据库内存中预分配的序列值个数，最小cache值为2 |不指定缓存数
默认值是cache 20
[ORDER | NOORDER] --指定order条件保证序列按请求顺序生成|不保证序列按请求顺序生成
默认值是NOORDER
单机 sequence都是order的。就算加了noorder，结果还是order。
RAC sequence才有真正的order和noorder
order：两个节点保持一样的order
noorder：如果使用了nocache，两个节点保持一样的order
如果使用了cache，两个节点不order，但各节点内部order
SQL> show parameter instance_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
instance_name string PLMDB2
SQL> create sequence SEQ_T1 start with 10 maxvalue 100000 cache 2000 noorder;
Sequence created.
SQL> select SEQ_T1.nextval from dual;
NEXTVAL
----------
10
SQL> select SEQ_T1.nextval from dual;
NEXTVAL
----------
11
SQL> show parameter instance_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
instance_name string PLMDB1
SQL> select SEQ_T1.nextval from dual;
NEXTVAL
----------
2010
SQL> select SEQ_T1.nextval from dual;
NEXTVAL
----------
2011
SQL> show parameter instance_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
instance_name string PLMDB2
SQL> create sequence SEQ_T2 start with 10 maxvalue 100000 nocache noorder;
Sequence created.
SQL> select SEQ_T2.nextval from dual;
NEXTVAL
----------
10
SQL> select SEQ_T2.nextval from dual;
NEXTVAL
----------
11
SQL> show parameter instance_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
instance_name string PLMDB1
SQL> select SEQ_T2.nextval from dual;
NEXTVAL
----------
12
SQL> select SEQ_T2.nextval from dual;
NEXTVAL
----------
13
SQL> show parameter instance_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
instance_name string PLMDB2
SQL> create sequence SEQ_T3 start with 10 maxvalue 100000 noorder;
Sequence created.
SQL> select SEQ_T3.nextval from dual;
NEXTVAL
----------
10
SQL> select SEQ_T3.nextval from dual;
NEXTVAL
----------
11
SQL> show parameter instance_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
instance_name string PLMDB1
SQL> select SEQ_T3.nextval from dual;
NEXTVAL
----------
30
SQL> select SEQ_T3.nextval from dual;
NEXTVAL
----------
31
SQL> show parameter instance_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
instance_name string PLMDB2
SQL> create sequence SEQ_T4 start with 10 maxvalue 100000 order;
Sequence created.
SQL> select SEQ_T4.nextval from dual;
NEXTVAL
----------
10
SQL> select SEQ_T4.nextval from dual;
NEXTVAL
----------
11
SQL> show parameter instance_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
instance_name string PLMDB1
SQL> select SEQ_T4.nextval from dual;
NEXTVAL
----------
12
SQL> select SEQ_T4.nextval from dual;
NEXTVAL
----------
13
