in 12/this year, when patient 99747 was prescribed for the first time a drug?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 99747 ) and datetime(prescriptions.startdate,'start of year') = datetime(current_time,'start of year','-0 year') and strftime('%m',prescriptions.startdate) = '12' order by prescriptions.startdate asc limit 1