instruction: calculate the number of patients who have been prescribed nss 0.9% 1,000 ml bolus infusion since 1 year ago.
response: SELECT COUNT(DISTINCT patient.uniquepid) FROM patient WHERE patient.patientunitstayid IN (SELECT medication.patientunitstayid FROM medication WHERE medication.drugname = 'nss 0.9% 1,000 ml bolus infusion' AND DATETIME(medication.drugstarttime) >= DATETIME(CURRENT_TIME(), '-1 year'))