ตั้งแต่ 113 วันที่ผ่านมา ให้แสดงรายการ sao2 เฉลี่ยรายเดือนของผู้ป่วย 031-11804 ไม่จำเป็นต้องใช้ตารางทั้งหมด
since 113 days ago, list the monthly average sao2 of patient 031-11804.It is not neccessary to use all the tables.
 patient:  uniquepid [ text]  patienthealthsystemstayid [ number]  patientunitstayid [ number]  gender [ text]  age [ text]  ethnicity [ text]  hospitalid [ number]  wardid [ number]  admissionheight [ number]  admissionweight [ number]  dischargeweight [ number]  hospitaladmittime [ time]  hospitaladmitsource [ text]  unitadmittime [ time]  unitdischargetime [ time]  hospitaldischargetime [ time]  hospitaldischargestatus [ text] 
SELECT AVG(vitalperiodic.sao2) FROM vitalperiodic WHERE vitalperiodic.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '031-11804')) AND NOT vitalperiodic.sao2 IS NULL AND DATETIME(vitalperiodic.observationtime) >= DATETIME(CURRENT_TIME(), '-113 day') GROUP BY STRFTIME('%y-%m', vitalperiodic.observationtime)