instruction: since 148 months ago, when was the first time that patient 16549 was prescribed both sterile water and sw at the same time?
response: SELECT t1.startdate FROM (SELECT admissions.subject_id, prescriptions.startdate FROM prescriptions JOIN admissions ON prescriptions.hadm_id = admissions.hadm_id WHERE prescriptions.drug = 'sterile water' AND admissions.subject_id = 16549 AND DATETIME(prescriptions.startdate) >= DATETIME(CURRENT_TIME(), '-148 month')) AS t1 JOIN (SELECT admissions.subject_id, prescriptions.startdate FROM prescriptions JOIN admissions ON prescriptions.hadm_id = admissions.hadm_id WHERE prescriptions.drug = 'sw' AND admissions.subject_id = 16549 AND DATETIME(prescriptions.startdate) >= DATETIME(CURRENT_TIME(), '-148 month')) AS t2 ON t1.subject_id = t2.subject_id WHERE DATETIME(t1.startdate) = DATETIME(t2.startdate) ORDER BY t1.startdate LIMIT 1