instruction: what was the last time patient 028-47306 had sedative agent's performed when they came to the hospital first time?
response: SELECT treatment.treatmenttime FROM treatment WHERE treatment.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '028-47306' AND NOT patient.hospitaldischargetime IS NULL ORDER BY patient.hospitaladmittime LIMIT 1)) AND treatment.treatmentname = 'sedative agent' ORDER BY treatment.treatmenttime DESC LIMIT 1