instruction: when was for the last time during the last hospital encounter patient 31696 prescribed a medication via po/ng route?
response: SELECT prescriptions.startdate FROM prescriptions WHERE prescriptions.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 31696 AND NOT admissions.dischtime IS NULL ORDER BY admissions.admittime DESC LIMIT 1) AND prescriptions.route = 'po/ng' ORDER BY prescriptions.startdate DESC LIMIT 1