instruction: how many times is warfarin sodium 5 mg po tabs ordered for patient 028-50921 since 2100?
response: SELECT COUNT(*) FROM medication WHERE medication.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '028-50921')) AND medication.drugname = 'warfarin sodium 5 mg po tabs' AND STRFTIME('%y', medication.drugstarttime) >= '2100'