instruction: on 07/19/2104, what was first value of sao2 for patient 2004?
response: SELECT 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 = 2004)) 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-%d', chartevents.charttime) = '2104-07-19' ORDER BY chartevents.charttime LIMIT 1