SELECT a1.patient_id, CAST(JULIANDAY(a2.admission_date) - JULIANDAY(a1.discharge_date) AS INT) as days_diff FROM admissions a1 JOIN admissions a2 ON a1.patient_id = a2.patient_id AND a2.admission_date > a1.discharge_date WHERE (JULIANDAY(a2.admission_date) - JULIANDAY(a1.discharge_date)) <= 30;
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