挿入と更新で同じ値を持つPostgreSQLアップサート（競合時）

INSERT INTO cars 
  (car_id, car_type, car_model) 
values
  (1, 'tesla', 'model s')
ON CONFLICT (car_id) DO UPDATE SET 
  car_type = excluded.car_type,
  car_model = excluded.car_model;

これは、複数の行でも正しく機能します（例：

INSERT INTO cars 
  (car_id, car_type, car_model) 
values
  (1, 'tesla', 'model s'), 
  (2, 'toyota', 'prius')
ON CONFLICT (car_id) DO UPDATE SET 
  car_type = excluded.car_type,
  car_model = excluded.car_model;