คำนวณจำนวนอินพุตที่ผู้ป่วย 18757 มี ไม่จำเป็นต้องใช้ตารางทั้งหมด
calculate the number of inputs patient 18757 had.It is not neccessary to use all the tables.
 labevents:  row_id [ number]  subject_id [ number]  hadm_id [ number]  itemid [ number]  charttime [ time]  valuenum [ number]  valueuom [ text] 
SELECT SUM(inputevents_cv.amount) FROM inputevents_cv WHERE inputevents_cv.icustay_id IN (SELECT icustays.icustay_id FROM icustays WHERE icustays.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 18757))