Time-Window Top Products Query | Dataford Interview Questions

Write a query to identify top-performing products based on specific time-window criteria at Wayfair.

Use completed orders from the current 30-day window, 2025-01-01 through 2025-01-30, and compare them with the preceding 30-day window, 2024-12-02 through 2024-12-31. Return the three products with the highest current-window revenue.

Output

One row per qualifying product with product_id, product_name, current_revenue, previous_revenue, and revenue_change_percent
Include products with no previous-window revenue, representing the percentage as NULL
Sort by current_revenue descending, then product_id ascending

Schema

products

Column	Type	Description
product_idPK	INT	Unique product identifier
product_name	VARCHAR(150)	Wayfair product name
category	VARCHAR(80)	Product category

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
order_date	DATE	Date the order was placed
order_status	VARCHAR(20)	Order status, such as completed or cancelled

order_items

Column	Type	Description
order_item_idPK	INT	Unique order-line identifier
order_id	INT	Referenced order
product_id	INT	Referenced product
quantity	INT	Units purchased
unit_price	NUMERIC(10,2)	Price per unit at order time

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