在Oracle数据库里创建自增ID字段的步骤

create table demo(
did varchar2(20)   constraint pk_demo primary key,
dname varchar2(20),
bumen varchar2(100)
)

create sequence demo_did_seq minvalue 1 nomaxvalue increment by 1 start with 1 nocache;

create or replace trigger demo_ins_trg
before insert
on demo
for each row when(new.did is null)
begin
select demo_did_seq.nextval into :new.did from dual;
end;
/