create or replace trigger userupdate

  after insert or update or delete on users

  for each row

begin

  if inserting then

    insert into user_log

      (description, user_id, new_user_name,update_time)

    values

      ('inserting', :new.user_id, :new.user_name,sysdate);

  else if updating then

    insert into user_log

      (description, user_id, old_user_name, new_user_name,update_time)

    values

      ('updating', :new.user_id, :old.user_name, :new.user_name,sysdate);

  else insert

      into user_log(description, user_id, new_user_name,update_time) values('deleting',:old.user_id,:old.user_name,sysdate);

  end if;

end userupdate;