Postgresql存储过程中基于会话的全局变量？

CREATE OR REPLACE FUNCTION track_login_count()
RETURNS TRIGGER AS $$
DECLARE
  user_id INTEGER;
BEGIN
  user_id := NEW.user_id;
  IF EXISTS (SELECT 1 FROM user_login_count WHERE user_id = user_id) THEN
    UPDATE user_login_count SET login_count = login_count + 1 WHERE user_id = user_id;
  ELSE
    INSERT INTO user_login_count (user_id, login_count) VALUES (user_id, 1);
  END IF;
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;