CREATE OR REPLACE TRIGGER CORE_MANUAL_BIUR
  BEFORE INSERT OR UPDATE ON CORE_MANUAL
  FOR EACH ROW
BEGIN
  if inserting then
    -- only set the current date if it is not specified        
    if :new.created is null then
      :new.created := sysdate;
    end if;
  end if;

  -- always set the modified date to now
  if inserting or updating then
    :new.modified := sysdate;
  end if;
end;
/