30-Day Readmission by Hospital | Dataford Interview Questions

Write a SQL query to join patient, admission, and discharge tables and calculate 30-day readmission rates by hospital. Count an admission as a readmission when the same patient is admitted again after discharge and within 30 calendar days. Use only admissions with a matching discharge record.

Output

One row per hospital, with columns hospital_name, completed_admissions, readmissions_30_day, and readmission_rate_pct
Include hospitals with completed admissions, ordered by hospital_name ascending
Return the rate as a percentage rounded to two decimal places

Schema

patient

Column	Type	Description
patient_idPK	INT	Unique patient identifier
patient_name	VARCHAR(100)	Patient's name
gender	VARCHAR(20)	Recorded gender

admission

Column	Type	Description
admission_idPK	INT	Unique admission identifier
patient_id	INT	Patient associated with the admission
hospital_name	VARCHAR(100)	Hospital where the admission occurred
admit_date	DATE	Admission date

discharge

Column	Type	Description
discharge_idPK	INT	Unique discharge record identifier
admission_id	INT	Admission associated with the discharge
discharge_date	DATE	Date the patient was discharged

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