Month-over-Month Utilization Comparison | Dataford Interview Questions

Write a SQL query to compare each patient's current-month utilization against their previous-month utilization at Optum Technology. Use the provided patient and utilization data. Ignore utilization records with a NULL service date, and treat NULL utilization units as zero.

Output

One row per patient whose current month immediately follows a month with recorded utilization.
Return patient_id, patient_name, current_month, current_utilization, previous_utilization, utilization_change, and percent_change.
Order by patient_id, then current_month ascending. If the previous utilization is zero, return NULL for percent_change.

Schema

patients

Column	Type	Description
patient_idPK	INT	Unique patient identifier
patient_name	VARCHAR(100)	Patient's display name

utilization_records

Column	Type	Description
utilization_idPK	INT	Unique utilization record identifier
patient_id	INT	Patient associated with the utilization record
service_date	DATE	Date on which utilization occurred
utilization_units	NUMERIC(10,2)	Units of healthcare utilization

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