Top Clients Per Region | Dataford Interview Questions

Your question is Top Clients Per Region. Start with the requirements and the three tables on the right.

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Problem

Insight Global needs a quarterly billing report for client leadership. Assume the reporting date is July 15, 2025, so the last completed quarter is April 1 through June 30, 2025.

Write a PostgreSQL query to identify the top three highest-billing clients within each region.

Requirements

Join invoices to clients and regions.
Include only invoices from the last completed quarter, using an inclusive start date and exclusive end date.
Aggregate invoice amounts by client and region.
Rank clients within each region and return no more than three clients per region, ordered by region and billing amount descending.

Schema

regions

Column	Type	Description
region_idPK	INT	Unique region identifier
region_name	VARCHAR(50)	Display name of the region

clients

Column	Type	Description
client_idPK	INT	Unique client identifier
client_name	VARCHAR(100)	Client organization name
region_id	INT	Region assigned to the client

invoices

Column	Type	Description
invoice_idPK	INT	Unique invoice identifier
client_id	INT	Client billed by the invoice
invoice_date	DATE	Date the invoice was issued
invoice_amount	NUMERIC(12,2)	Invoice amount in dollars