Window Ranking for Customers | Dataford Interview Questions

Publicis Groupe México wants to identify the highest-value customers within each product category for audience planning and campaign prioritization. Write a PostgreSQL query using joins, aggregation, and a window function.

Requirements

Consider only orders with order_status = 'completed'.
Calculate each customer's total completed order value within each product category, treating NULL order amounts as zero.
Rank customers independently within each category by total value in descending order.
Return only the top three customers per category, ordered by category, rank, and customer ID.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer's full name

products

Column	Type	Description
product_idPK	INT	Unique product identifier
category	VARCHAR(50)	Product category
product_name	VARCHAR(100)	Product name

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
customer_id	INT	Customer who placed the order
product_id	INT	Product included in the order
order_amount	NUMERIC(10,2)	Monetary value of the order
order_status	VARCHAR(20)	Order state

Your question is Window Ranking for Customers. Start with the requirements and the three tables in the Question tab.

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Problem