instruction: calculate the number of patients who have been prescribed zofran during this year.
response: SELECT COUNT(DISTINCT patient.uniquepid) FROM patient WHERE patient.patientunitstayid IN (SELECT medication.patientunitstayid FROM medication WHERE medication.drugname = 'zofran' AND DATETIME(medication.drugstarttime, 'start of year') = DATETIME(CURRENT_TIME(), 'start of year', '-0 year'))