Top Customers Per Region | Dataford Interview Questions

Abzooba needs a regional revenue leaderboard for its customer analytics platform. Assume the reporting date is 2025-03-31, and the last 30 days means 2025-03-02 through 2025-03-31, inclusive. Write a PostgreSQL query to identify the top three customers by completed-order revenue in each region.

Requirements

Join customers to regions and orders.
Include only completed orders within the stated 30-day window.
Calculate revenue as quantity * unit_price per customer, treating missing revenue as zero.
Rank customers independently within each region and return at most three per region.
Sort by region, revenue descending, and customer ID as a deterministic tie-breaker.

Schema

regions

Column	Type	Description
region_idPK	INT	Unique region identifier
region_name	VARCHAR(50)	Display name of the region

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer full name
region_id	INT	Region assigned to the customer

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
customer_id	INT	Customer associated with the order
order_date	DATE	Date on which the order was placed
status	VARCHAR(20)	Order processing status
quantity	INT	Number of units ordered
unit_price	NUMERIC(10,2)	Price per ordered unit

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