calculate the number of medications that are prescribed to patient 19894 in 06/last year.
select count(*) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 19894 ) and datetime(prescriptions.startdate,'start of year') = datetime(current_time,'start of year','-1 year') and strftime('%m',prescriptions.startdate) = '06'