instruction: what were the top three most common diagnoses of patients aged 30s until 2102.
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 30 AND 39) AND STRFTIME('%y', diagnosis.diagnosistime) <= '2102' GROUP BY diagnosis.diagnosisname) AS t1 WHERE t1.c1 <= 3