MoM Active Borrower Growth | Dataford Interview Questions

Write a query to find the month-over-month growth rate of active borrowers on the Happy Money platform.

Use the provided borrower and activity data. Treat a borrower as active for a month when they have an activity row marked active and a matching platform borrower record with platform_status = 'active'.

Output

One row per calendar month represented in the activity data.
Columns: month, active_borrowers, prior_month_active_borrowers, and growth_rate_pct.
Calculate growth as the percentage change from the immediately preceding calendar month. Return NULL when no prior-month count exists.
Order by month ascending.

Schema

borrowers

Column	Type	Description
borrower_idPK	INT	Unique Happy Money borrower identifier
created_at	DATE	Date the borrower joined the platform
platform_status	VARCHAR(20)	Current platform status of the borrower

borrower_activity

Column	Type	Description
activity_idPK	INT	Unique activity record identifier
borrower_id	INT	Borrower associated with the activity
activity_date	DATE	Date of the borrower activity
activity_status	VARCHAR(20)	Whether the activity qualifies as active

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Problem