oracle建触发器与创建递增字段

////建表
create table test (
  user_id   NUMBER(7) not null,
  user_name VARCHAR2(20) not null,
  password  VARCHAR2(20) not null,
  department VARCHAR2(20) not null,
  remark VARCHAR2(200),
constraint PK_test2 primary key (user_id)
)
////产生sequence
create sequence Seq_test
increment by 1
start with 1
nomaxvalue
minvalue 0
nocycle
cache 20
noorder
/////产生trigger
create trigger trg_test before insert on test for each row
declare
integrity_error exception;
errno integer;
errmsg char(200);
dummy integer;
found boolean;
begin
select Seq_test.NEXTVAL INTO :new.user_id from dual;
exception
when integrity_error then