SQL for Top Usage Customers | Dataford Interview Questions

Write a SQL query to find the top 10% of customers by usage volume over the last 30 days at Infoblox.

Assume usage volume is stored in usage_events.usage_volume. Include customers with no qualifying usage as zero, and use the current date to define the 30-day period.

Output

One row per qualifying customer with customer_id, customer_name, and total_usage.
Include only the top 10% of customers, rounded up to at least one customer.
Order by total_usage descending, then customer_id ascending for ties.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique Infoblox customer identifier
customer_name	VARCHAR(150)	Customer organization name
plan_name	VARCHAR(50)	Infoblox subscription plan

usage_events

Column	Type	Description
event_idPK	INT	Unique usage event identifier
customer_id	INT	Customer associated with the usage event
usage_date	DATE	Date on which usage occurred
usage_volume	DECIMAL(14,2)	Usage volume recorded for the event

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Problem