what are the four most frequent drugs that were prescribed within the same month to the male patients with age 30s after they have been diagnosed with crnry athrscl natve vssl, since 6 years ago.
select t3.drug from ( select t2.drug, dense_rank() over ( order by count(*) desc ) as c1 from ( select admissions.subject_id, diagnoses_icd.charttime from diagnoses_icd join admissions on diagnoses_icd.hadm_id = admissions.hadm_id where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'crnry athrscl natve vssl' ) and datetime(diagnoses_icd.charttime) >= datetime(current_time,'-6 year') ) as t1 join ( select admissions.subject_id, prescriptions.drug, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where admissions.subject_id in ( select patients.subject_id from patients where patients.gender = 'm' ) and admissions.age between 30 and 39 and datetime(prescriptions.startdate) >= datetime(current_time,'-6 year') ) as t2 on t1.subject_id = t2.subject_id where t1.charttime < t2.startdate and datetime(t1.charttime,'start of month') = datetime(t2.startdate,'start of month') group by t2.drug ) as t3 where t3.c1 <= 4