触发器实现表id的自动增长

/*==========创建***表序列触发器==========*/

--首先创建一个触发器
create sequence seq_***_ids
minvalue 1
maxvalue 99999999
start with 1
increment by 1
nocache;

--创建触发器
create or replace
trigger tri_***_id
before insert
on ***   --表名
for each row
declare
nextid number;
begin
  if :new.id is null or :new.id=0 then
     select seq_***_ids.nextval
     into nextid
      from dual;
      :new.id:=nextid;
  end if;
end tri_***_id;