ผู้ป่วยหญิงอายุต่ำกว่า 67 ปี จำนวนกี่ราย ไม่จำเป็นต้องใช้ทุกโต๊ะ
how many female patients are under 67 years of age?It is not neccessary to use all the tables.
 lab:  subject_id [ text]  hadm_id [ text]  itemid [ text]  charttime [ text]  flag [ text]  value_unit [ text]  label [ text]  fluid [ text] 
SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic WHERE demographic.gender = "F" AND demographic.age < "67"