Window Functions for Top Per Group | Dataford Interview Questions

Write a SQL query using window functions to rank customers or events within each group and return the top record per group.

Use the provided customers and events tables. Calculate each active customer's total value from completed events, rank customers within their region, and resolve ties by the lowest customer_id.

Output

One row per region, containing region, customer_id, customer_name, total_event_value, and customer_rank.
Include only the top-ranked active customer in each region, ordered by region.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name
region	VARCHAR(50)	Customer region
is_active	BOOLEAN	Whether the customer is active

events

Column	Type	Description
event_idPK	INT	Unique event identifier
customer_id	INT	Customer associated with the event
event_date	DATE	Date of the event
event_status	VARCHAR(20)	Event processing status
event_value	NUMERIC(10,2)	Value attributed to the event

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Problem