MoM Growth of Active API Users | Dataford Interview Questions

Write a query to calculate the month-over-month growth rate of active API users, defining active as having at least three successful API calls in a calendar month.

Use the users and api_calls tables. Report only months with a preceding calendar month that also has active users.

Output

One row per eligible calendar month.
Columns: month_start, active_users, previous_active_users, and growth_rate_pct.
Calculate growth as (active_users - previous_active_users) / previous_active_users * 100, rounded to two decimal places.
Order by month_start ascending.

Schema

users

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

api_calls

Column	Type	Description
call_idPK	INT	Unique API call identifier
user_id	INT	User that made the API call
called_at	TIMESTAMP	Timestamp when the API call occurred
status	VARCHAR(20)	API call result status

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Problem