MoM Growth of Active Therapists | Dataford Interview Questions

Write a query to find the month-over-month growth rate of active therapists on Headway.

Treat a therapist as active when is_active is true for that month. Calculate growth only for months with a preceding calendar month, and avoid division by zero.

Output

One row per month with a preceding month
Columns: month, active_therapists, previous_active_therapists, and growth_rate_pct
Sort chronologically by month

Schema

reporting_months

Column	Type	Description
month_startPK	DATE	First day of a reporting calendar month

therapist_monthly_activity

Column	Type	Description
activity_idPK	INT	Unique monthly activity record
therapist_id	INT	Therapist identifier
month_start	DATE	Reporting month for the activity record
is_active	BOOLEAN	Whether the therapist was active during the month

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