create table Test_Increase(

           userid number(10) NOT NULL primary key,  /*主键，自动增加*/

           username varchar2(20)

           );

 CREATE SEQUENCE TestIncrease_Sequence

 INCREMENT BY 1   -- 每次加几个

     START WITH 1     -- 从1开始计数

     NOMAXVALUE       -- 不设置最大值  ，设置最大值：maxvalue 9999

     NOCYCLE          -- 一直累加，不循环

     CACHE 10; 

CREATE TRIGGER Test_Increase BEFORE

insert ON  Test_Increase FOR EACH ROW          /*对每一行都检测是否触发*/

begin

select TestIncrease_Sequence.nextval into:New.userid from dual;

end;

/       /*退出sqlplus行编辑*/

insert into Test_Increase(Username) values('test');