I have a postgres database and also I have a table called product. In this table I have an autoincrement column named auxId (not table primary key). I want to avoid any update on this column. How can this be done using a postgres trigger to avoid updates on auxid? I tried:

```
   #trigger to avoid updates on nameId
CREATE OR REPLACE FUNCTION stop_change_on_auxId()
  RETURNS trigger AS
$BODY$
BEGIN
 IF NEW.auxId <> OLD.auxId THEN

 END IF;

 RETURN NEW;
END;
$BODY$

CREATE TRIGGER avoid_auxid_changes
  BEFORE UPDATE
  ON product
  FOR EACH ROW
  EXECUTE PROCEDURE stop_change_on_auxId();

```

but I believe this will stop the update for the whole row. I just need to avoid the update on the auxId field but allow any other update on its row.