create sequence seq_forum_id
increment by 1
start with 1;

create table t_forum  (
   forum_id           int                             not null,
   forum_name         varchar2(100)                  default '' not null,
   forum_desc         varchar2(100)                  default NULL,
   constraint pk_t_forum primary key (forum_id)
);

create or replace trigger tri_forum_id
  before insert on t_forum for each row
declare
  -- local variables here
  nextID int;
  begin
	  select seq_forum_id.nextVal into nextID from dual;
	  :new.forum_id:=nextID;    
  end tri_forum_id;
  
/