instruction: indicate the yearly average amount of sao2 for patient 28447 since 12/2105.
response: SELECT AVG(chartevents.valuenum) FROM chartevents WHERE chartevents.icustay_id IN (SELECT icustays.icustay_id FROM icustays WHERE icustays.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 28447)) AND chartevents.itemid IN (SELECT d_items.itemid FROM d_items WHERE d_items.label = 'sao2' AND d_items.linksto = 'chartevents') AND STRFTIME('%y-%m', chartevents.charttime) >= '2105-12' GROUP BY STRFTIME('%y', chartevents.charttime)