postgresql - Triger update function when column updates in Postgres -

i have users table columns status_id (int), additional_status(int) , status_changed(date).

i want autoupdate status_changed field every time when status_id or additional_status changes.

here have now:

    create or replace function update_status_changed() returns trigger  $$ begin   new.status_changed := current_timestamp;    return new; end $$ language plpgsql;  create trigger set_update_status_changed after insert or update of status_id, additional_status on users each row    execute procedure update_status_changed(); 

i'm not sure if syntax correct. when change status_id phppgadmin - status_changed stays null. i'm missing?, pls.