مسارات وأدلة برمجية بالعربية، مرتّبة خطوة بخطوة

CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT NOT NULL
);
INSERT INTO orders (id, customer_id) VALUES
(1, 10), (2, 10), (3, 20), (4, 20);

SELECT id,
       ROW_NUMBER() OVER (
         PARTITION BY customer_id
         ORDER BY id
       ) AS rn
FROM orders
ORDER BY id;