CREATE OR REPLACE FUNCTION cleanNoteEventConnections() RETURNS TRIGGER AS $$
DECLARE
BEGIN
    EXECUTE 'update invoice set "noteEvent"=null where "noteEvent"=' || OLD.id;
RETURN NULL;
END;
$$ LANGUAGE 'plpgsql';

CREATE TRIGGER cleanNoteEventConnections BEFORE DELETE ON note_event
    FOR EACH ROW EXECUTE PROCEDURE cleanNoteEventConnections();