หาจำนวนผู้ป่วยหญิงที่เกิดก่อนปี 2197 ไม่จำเป็นต้องใช้ตารางทั้งหมด
find the number of female patients whose year of birth is before 2197.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.dob_year < "2197"