Order lines with product and category names

An operations analyst needs a readable list of the bigger order lines, with the product and category names instead of IDs.

Join order_items, products and categories. Return order_id, product_name, category_name, quantity and line_total (quantity * unit_price) for lines whose line_total is 2000 or more. Order by line_total descending, then item_id.

1. Step 1: Start from `order_items` and join `products` on `product_id`.
2. Step 2: Chain a second join from `products` to `categories` on `category_id`; each `JOIN` adds one table to the running result.
3. Step 3: `WHERE` cannot reference the `line_total` alias, so the expression is repeated; `ORDER BY` can use the alias.

SELECT oi.order_id,
       p.product_name,
       c.category_name,
       oi.quantity,
       oi.quantity * oi.unit_price AS line_total
FROM order_items oi
JOIN products   p ON p.product_id  = oi.product_id
JOIN categories c ON c.category_id = p.category_id
WHERE oi.quantity * oi.unit_price >= 2000
ORDER BY line_total DESC, oi.item_id;