Top Clinics by Patient Volume | Dataford Interview Questions

Oracle Health EHR operations leaders need a ranked view of clinic utilization. Write a PostgreSQL query to identify the five clinics with the highest patient volume during calendar year 2025.

Requirements

Join clinics to visits and consider only visits with visit_status = 'completed' from 2025.
Calculate patient volume as the number of distinct non-null patients per clinic, so repeat visits by one patient count once.
Use a window function to assign a deterministic rank, returning exactly the top five clinics. Break volume ties by the smaller clinic_id.
Return clinic_name, city, patient_volume, and clinic_rank, ordered by rank.

Schema

clinics

Column	Type	Description
clinic_idPK	INTEGER	Unique clinic identifier
clinic_name	VARCHAR(100)	Oracle Health EHR clinic name
city	VARCHAR(80)	Clinic city

visits

Column	Type	Description
visit_idPK	INTEGER	Unique visit identifier
clinic_id	INTEGER	Associated clinic identifier
patient_id	INTEGER	Patient identifier
visit_date	DATE	Date of the visit
visit_status	VARCHAR(20)	Visit completion status

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