Well done! In business reports, we often want to calculate certain metrics for multiple business objects at the same time. For instance:

SELECT
  o.order_id,
  COUNT(*) AS order_items_count
FROM orders o
JOIN order_items oi
  ON o.order_id = oi.order_id
WHERE o.order_id BETWEEN 10200 AND 10300
GROUP BY o.order_id;

In the query above, we count the number of items in each order with an order_id in the specified range. By joining the orders and order_items tables, we can display information about a single order item and its parent order on the same row. Then, we group all rows by their parent order and use COUNT(*) to find the number of items in each order.