CREATE SEQUENCE 语句用来创建序列，语法格式如下：

    1. CREATE SEQUENCE sequence_name
    2.   [MINVALUE value | NOMINVALUE]
    3.   [MAXVALUE value | NOMAXVALUE]
    4.   [START WITH value]
    5.   [INCREMENT BY value]
    6.   [CACHE value | NOCACHE]
    7.   [ORDER | NOORDER]
    8.   [CYCLE | NOCYCLE];

    其中，MINVALUE 和 MAXVALUE 指定最小值和最大值；START WITH 指定起始值；INCREMENT BY 指定步长，可以为负数，默认是1；CACHE 是为了性能缓存部分序列值，并发高的时候使用；CYCLE 指定序列值是否循环，如果循环，需要指定最大值或最小值。

    示例：创建序列，实现表的列自增。

    1. obclient> create table t1(id number not null primary key, name varchar(50) , gmt_create date not null default sysdate);
    2. Query OK, 0 rows affected (0.07 sec)
    4. obclient> create sequence seq_t1 start with 10000 increment by 1 cache 50 nocycle;
    5. Query OK, 0 rows affected (0.04 sec)
    7. obclient> insert into t1(id,name) values(seq_t1.nextval, 'A');
    8. Query OK, 1 row affected (0.02 sec)
    10. obclient> insert into t1(id,name) values(seq_t1.nextval, 'B');
    11. Query OK, 1 row affected (0.00 sec)
    13. obclient> insert into t1(id,name) values(seq_t1.nextval, 'C');
    14. Query OK, 1 row affected (0.00 sec)
    16. obclient> select * from t1;
    17. +-------+------+---------------------+
    18. | ID    | NAME | GMT_CREATE          |
    19. +-------+------+---------------------+
    20. | 10000 | A    | 2020-04-02 18:30:29 |
    21. | 10001 | B    | 2020-04-02 18:30:34 |
    22. | 10002 | C    | 2020-04-02 18:30:39 |
    23. +-------+------+---------------------+
    24. 3 rows in set (0.01 sec)

    序列创建成功后，可以通过 USER_SEQUENCES、ALL_SEQUENCES、DBA_SEQUENCES 视图查看自己创建的序列。

    1. obclient> select * from user_sequences \G
    2. *************************** 1. row ***************************
    3. SEQUENCE_NAME: SEQ_T1
    4.     MIN_VALUE: 1
    5.     MAX_VALUE: 9999999999999999999999999999
    6.  INCREMENT_BY: 1
    7.    CYCLE_FLAG: N
    8.    ORDER_FLAG: N
    9.    CACHE_SIZE: 50
    10.   LAST_NUMBER: 10100
    11. 1 row in set (0.00 sec)
    12. obclient>