instruction: what is patient 006-21143's last ward id since 3 years ago?
response: SELECT patient.wardid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '006-21143') AND DATETIME(patient.unitadmittime) >= DATETIME(CURRENT_TIME(), '-3 year') ORDER BY patient.unitadmittime DESC LIMIT 1