tell me the total bag dose that patient 9338 has been prescribed until 07/2104?
select sum(prescriptions.dose_val_rx) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 9338 ) and prescriptions.drug = 'bag' and strftime('%y-%m',prescriptions.startdate) <= '2104-07'