Top 10% Data Usage Query | Dataford Interview Questions

McAfee wants to identify users with the highest recent data consumption. Write a SQL query that calculates each user's total data usage during the 30-day period ending on September 15, 2026, and returns the top 10% of users.

Output

One row per selected user, with columns user_id, username, total_usage_bytes, and usage_rank
Include every user in the population when calculating the 10% cutoff, including users with no qualifying events, whose total is treated as zero
Include events from August 17, 2026 through September 15, 2026, inclusive; ignore events outside this period and events with NULL user_id
Round the cutoff up to the next whole user, so a nonempty population returns at least one user
Sort by usage_rank, then user_id; rank ties deterministically by ascending user_id
Rows with NULL usage_bytes contribute nothing to a user's total

Schema

users

Column	Type	Description
user_idPK	INT	Unique McAfee user identifier
username	VARCHAR(100)	User display name
email	VARCHAR(255)	User email address

usage_events

Column	Type	Description
event_idPK	INT	Unique usage event identifier
user_id	INT	User associated with the usage event
event_timestamp	TIMESTAMP	Time when the data usage occurred
usage_bytes	BIGINT	Bytes used during the event

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