instruction: calculate how many drugs patient 021-100763 is prescribed on this hospital visit.
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 = '021-100763' AND patient.hospitaldischargetime IS NULL))