Month-over-Month Active Patient Growth | Dataford Interview Questions

Write a query to find the month-over-month growth rate of active patients booking appointments on Zocdoc.

Use the patients and appointments tables. Treat an active patient as one whose is_active value is true and who has at least one appointment with a booked status in the month.

Output

One row per calendar month with booking activity
Columns: month, active_patient_count, previous_active_patient_count, and mom_growth_rate
Express mom_growth_rate as a percentage rounded to two decimal places; return NULL when there is no prior month or the prior count is zero
Sort chronologically by month

Schema

patients

Column	Type	Description
patient_idPK	INT	Unique patient identifier
patient_name	VARCHAR(100)	Patient display name
is_active	BOOLEAN	Whether the patient is currently active

appointments

Column	Type	Description
appointment_idPK	INT	Unique appointment identifier
patient_id	INT	Patient associated with the appointment
booked_at	TIMESTAMP	Timestamp when the appointment was booked
status	VARCHAR(20)	Appointment booking status

Your question is Month-over-Month Active Patient Growth. Start with the requirements and the two tables in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem