instruction: tell me the top five of the most common diagnoses of patients 20s since 4 years ago?
response: SELECT t1.diagnosisname FROM (SELECT diagnosis.diagnosisname, DENSE_RANK() OVER (ORDER BY COUNT(*) DESC) AS c1 FROM diagnosis WHERE diagnosis.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.age BETWEEN 20 AND 29) AND DATETIME(diagnosis.diagnosistime) >= DATETIME(CURRENT_TIME(), '-4 year') GROUP BY diagnosis.diagnosisname) AS t1 WHERE t1.c1 <= 5