instruction: among the patients aged 20s , what was the top three most frequent diagnosis?
response: SELECT d_icd_diagnoses.short_title FROM d_icd_diagnoses WHERE d_icd_diagnoses.icd9_code IN (SELECT t1.icd9_code FROM (SELECT diagnoses_icd.icd9_code, DENSE_RANK() OVER (ORDER BY COUNT(*) DESC) AS c1 FROM diagnoses_icd WHERE diagnoses_icd.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.age BETWEEN 20 AND 29) GROUP BY diagnoses_icd.icd9_code) AS t1 WHERE t1.c1 <= 3)