Первичный ключ против внешнего ключа?

CREATE TABLE users (
  id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  email TEXT NOT NULL UNIQUE,
  name TEXT NOT NULL,
  city TEXT NOT NULL,
  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

CREATE TABLE orders (
  id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  user_id BIGINT NOT NULL REFERENCES users(id),
  status TEXT NOT NULL CHECK (status IN ('pending', 'completed', 'cancelled')),
  amount NUMERIC(12, 2) NOT NULL CHECK (amount >= 0),
  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

CREATE INDEX idx_orders_user_created ON orders (user_id, created_at DESC);