SQL Window Functions for Top Customers | Dataford Interview Questions

Your question is SQL Window Functions for Top Customers. Start with the requirements and the two tables on the right.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

Genesys Cloud Analytics needs a ranked view of customers based on completed subscription revenue. Write a PostgreSQL query that aggregates revenue per customer and uses a window function to return the top 10 customers.

Requirements

Join customers to orders using customer_id.
Include only orders with status = 'completed'.
Calculate total revenue per customer, treating a customer with only NULL revenue values as zero.
Use a window function to assign the revenue rank, return the top 10 ranks, and order the final result from highest to lowest revenue. Break ties by customer_id.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(120)	Customer account name
segment	VARCHAR(40)	Customer segment

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
customer_id	INT	References customers.customer_id
revenue	NUMERIC(12,2)	Revenue recognized for the order
status	VARCHAR(20)	Order processing status
order_date	DATE	Date the order was placed