SQL Top 5 Customers by Revenue | Dataford Interview Questions

Confluent's customer analytics team needs a ranked view of its highest-revenue customers. Assuming the reporting date is January 1, 2026, write a PostgreSQL query to find the top five customers by completed-order revenue during the previous calendar year, January 1 through December 31, 2025.

Requirements

Include only orders with status = 'completed' and an order_date in the 2025 calendar year.
Join qualifying orders to customers and aggregate revenue by customer.
Return the top five customers, ordered by revenue descending, with customer_id as a deterministic tie-breaker.

Schema

customers

Column	Type	Description
customer_idPK	INTEGER	Unique customer identifier
customer_name	VARCHAR(100)	Customer or organization name
segment	VARCHAR(30)	Customer segment

orders

Column	Type	Description
order_idPK	INTEGER	Unique order identifier
customer_id	INTEGER	Customer associated with the order
order_date	DATE	Date the order was placed
status	VARCHAR(20)	Order processing status
total_amount	NUMERIC(12,2)	Order revenue amount

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