instruction: what were the four most common diagnoses for patients who were aged 50s since 1 year 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 50 AND 59) AND DATETIME(diagnosis.diagnosistime) >= DATETIME(CURRENT_TIME(), '-1 year') GROUP BY diagnosis.diagnosisname) AS t1 WHERE t1.c1 <= 4