CREATE SEQUENCE 序列名
[INCREMENT BY n]
[START WITH n]
[{MAXVALUE/ MINVALUE n|NOMAXVALUE}]
[{CYCLE|NOCYCLE}]
[{CACHE n|NOCACHE}];

-- Create sequence
create sequence SEQ_T_RECV
minvalue 1
maxvalue 9999999
start with 1
increment by 1
cache 50;

-- Create table
create table RECV_MSG
(
 id     NUMBER,
 messageid  VARCHAR2(32),
 contents  VARCHAR2(2000),
 app_flg   VARCHAR2(100),
 phonenumber VARCHAR2(2000),
 updatetime DATE default sysdate
);

CREATE OR REPLACE TRIGGER "recv_trig"
 BEFORE INSERT ON recv_msg
 REFERENCING OLD AS OLD NEW AS NEW FOR EACH ROW
DECLARE
BEGIN
 SELECT SEQ_T_RECV.NEXTVAL INTO :NEW.ID FROM DUAL;
END recv_trig;

create sequence seq_on_test 
increment by 1 
start with 1 
nomaxvalue 
nocycle 
nocache; 

--建表 
drop table test; 
create table test( 
ID integer 
,stu_name nvarchar2(4) 
,stu_age number 
); 

--插入数据 
insert into test values(seq_on_test.nextval,'Mary',15); 
insert into test values(seq_on_test.nextval,'Tom',16); 
 

select * from test; 

--结果 
/* 
1 Mary 15 
2 Tom 16 
*/ 

--seq的两个方法 
select seq_on_test.currval from dual; 
select seq_on_test.nextval from dual; 

--结果 
/* 
2 
3 
*/