Rank Customers by Monthly Usage | Dataford Interview Questions

Write a SQL query to rank customers by monthly usage within each region at Viasat.

Use the provided customer and usage data. Include only customers with an assigned region and recorded usage, and treat a month as the calendar month of each usage record.

Output

One row per customer and calendar month.
Columns: region, usage_month, customer_id, customer_name, monthly_usage, and usage_rank.
Rank customers within their region and month by monthly usage descending. Ties share a rank.
Sort by region, usage_month, usage_rank, and customer_id.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name
region	VARCHAR(50)	Assigned Viasat service region

usage_records

Column	Type	Description
usage_idPK	INT	Unique usage record identifier
customer_id	INT	Customer associated with the usage record
usage_date	DATE	Date on which usage occurred
usage_units	NUMERIC(12,2)	Usage amount recorded for the customer

Your question is Rank Customers by Monthly Usage. Start with the requirements and the two tables in the Question tab.

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Problem