SQL for 30-Day ER Visits | Dataford Interview Questions

Write a SQL query to find all patients who had a specific spine procedure and subsequently visited the emergency room within 30 days.

Assume the specific procedure is identified by procedure_code = 'LUMBAR_FUSION'. Return only the earliest qualifying emergency room visit for each patient.

Output

One row per qualifying patient, with patient_id, patient_name, procedure_date, and er_visit_date.
Include only visits occurring after the procedure and no later than 30 days afterward.
Order by patient_id ascending.

Schema

patients

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

procedures

Column	Type	Description
procedure_idPK	INT	Unique procedure identifier
patient_id	INT	Patient receiving the procedure
procedure_code	VARCHAR(50)	Clinical procedure code
procedure_date	DATE	Date the procedure occurred

encounters

Column	Type	Description
encounter_idPK	INT	Unique encounter identifier
patient_id	INT	Patient associated with the encounter
visit_type	VARCHAR(50)	Type of healthcare encounter
visit_date	DATE	Date of the encounter

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