SQL Top 3 Customers Per Month | Dataford Interview Questions

Your question is SQL Top 3 Customers Per Month. Start with the requirements and the two tables on the right.

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Problem

PA Consulting wants a monthly view of its highest-value client accounts. Write a PostgreSQL query that calculates completed-order revenue for each client and returns the top three clients in every month.

Requirements

Join customers to orders using customer_id.
Include only orders with status = 'completed' and group revenue by calendar month and client.
Rank clients independently within each month using a deterministic ordering, then return ranks 1 through 3.
Return the month as YYYY-MM, client name, total revenue, and monthly rank, ordered by month and rank.

Schema

customers

Column	Type	Description
customer_idPK	INTEGER	Unique client identifier
customer_name	VARCHAR(120)	Client account name

orders

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