เมื่อในปี 05/ปีนี้เป็นการทดสอบ po2 ครั้งสุดท้ายของผู้ป่วย 3939 หรือไม่ ไม่จำเป็นต้องใช้ตารางทั้งหมด
when in 05/this year was patient 3939's last test for po2?It is not neccessary to use all the tables.
 transfers:  row_id [ number]  subject_id [ number]  hadm_id [ number]  icustay_id [ number]  eventtype [ text]  careunit [ text]  wardid [ number]  intime [ time]  outtime [ time] 
SELECT labevents.charttime FROM labevents WHERE labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'po2') AND labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 3939) AND DATETIME(labevents.charttime, 'start of year') = DATETIME(CURRENT_TIME(), 'start of year', '-0 year') AND STRFTIME('%m', labevents.charttime) = '05' ORDER BY labevents.charttime DESC LIMIT 1