instruction: for the patients with age 40s what are the top four most frequent diagnoses since 2104?
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 40 AND 49) AND STRFTIME('%y', diagnosis.diagnosistime) >= '2104' GROUP BY diagnosis.diagnosisname) AS t1 WHERE t1.c1 <= 4