Trigger - Technique 3

CREATE TABLE IF NOT EXISTS audit_log (
  id BIGSERIAL PRIMARY KEY,
  table_name TEXT,
  action TEXT,
  changed_at TIMESTAMPTZ DEFAULT now()
);

CREATE OR REPLACE FUNCTION log_user_update()
RETURNS TRIGGER AS $$
BEGIN
  INSERT INTO audit_log(table_name, action)
  VALUES ('users', 'UPDATE');
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trg_users_update
AFTER UPDATE ON users
FOR EACH ROW EXECUTE FUNCTION log_user_update();