ผู้ป่วยอายุต่ำกว่า 72 ปี จำนวนเท่าใด ไม่จำเป็นต้องใช้ทุกตาราง
what is the number of patients less than 72 years of age?It is not neccessary to use all the tables.
 prescriptions:  subject_id [ text]  hadm_id [ text]  icustay_id [ text]  drug_type [ text]  drug [ text]  formulary_drug_cd [ text]  route [ text]  drug_dose [ text] 
SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic WHERE demographic.age < "72"