SQL for 30-Day Readmission Rates | Dataford Interview Questions

Write a SQL query to calculate 30-day readmission rates by hospital unit from patient encounter data.

Use completed inpatient encounters as the denominator. A readmission occurs when the same patient has another inpatient admission after discharge and within 30 days of the index discharge date.

Output

One row per hospital unit, including units with no eligible encounters
Columns: unit_id, unit_name, eligible_discharges, readmissions_within_30_days, and readmission_rate_pct
Show the rate as a percentage rounded to two decimal places, with zero for units having no eligible discharges
Order by unit_id ascending

Schema

patient_encounters

Column	Type	Description
encounter_idPK	INT	Unique patient encounter identifier
patient_id	INT	Patient identifier
unit_id	INT	Hospital unit associated with the encounter
admission_date	DATE	Date the patient was admitted
discharge_date	DATE	Date the patient was discharged
encounter_type	VARCHAR(30)	Type of encounter, such as Inpatient or Observation
discharge_status	VARCHAR(30)	Disposition recorded at discharge

hospital_units

Column	Type	Description
unit_idPK	INT	Unique hospital unit identifier
unit_name	VARCHAR(100)	Hospital unit name

Your question is SQL for 30-Day Readmission Rates. 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