create table book(
bookId varchar2(4) primary key,
name varchar2(20)
);

--建立序列
create sequence book_seq start with 1 increment by 1;
--建立觸發器
create or replace trigger book_trigger
before insert on book
for each row
begin
select book_seq.nextval into :new.bookId from dual;
end ;
--新增資料
insert into
 
 book(name) values ('cc');
insert into book(name) values ('dd');
commit;

select * from book;

注意 :new.bookId 要為book表中的id的名稱 .

結果如圖