Top Customers Per Region SQL | Dataford Interview Questions

Engie Impact needs a regional view of its highest-consuming customers. Write a PostgreSQL query that aggregates energy consumption by month and ranks customers within each region.

Requirements

Join customer information with energy readings.
Calculate each customer's total consumption for every month in 2025.
Return the top three customers for each region and month, ranking ties by customer_id.
Return the region, month, customer, total consumption, and rank.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name
region	VARCHAR(50)	Customer's operating region

energy_consumption

Column	Type	Description
reading_idPK	INT	Unique energy reading identifier
customer_id	INT	Customer associated with the reading
reading_date	DATE	Date on which consumption was recorded
consumption_kwh	DECIMAL(12,2)	Energy consumption in kilowatt-hours

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