Active Subscriber Usage Query | Dataford Interview Questions

AT&T needs a January 2026 usage report for active subscribers. Write a PostgreSQL query that combines subscriber and plan data with usage events.

Requirements

Use an INNER JOIN between subscribers and plans, so only subscribers with a valid plan are reported.
Use a LEFT JOIN to retain active subscribers with no January usage before aggregation.
Report each active subscriber's name, plan, January data usage in gigabytes, and usage event count.
Use GROUP BY and HAVING to return only subscribers with at least 5,000 MB of January usage. Treat missing usage as zero, and order by usage descending.

subscribers

Column	Type	Description
subscriber_idPK	INT	Unique AT&T subscriber identifier
subscriber_name	VARCHAR(100)	Subscriber's full name
plan_id	INT	Assigned wireless plan
status	VARCHAR(20)	Subscriber account status

plans

Column	Type	Description
plan_idPK	INT	Unique wireless plan identifier
plan_name	VARCHAR(100)	AT&T wireless plan name

usage_events

Column	Type	Description
event_idPK	INT	Unique usage event identifier
subscriber_id	INT	Subscriber associated with the event
usage_date	DATE	Date when data was consumed
data_mb	NUMERIC(10,2)	Data consumed in megabytes

Your question is Active Subscriber Usage Query. Start with the requirements and the three tables in the Question tab.

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