ผู้ป่วยอายุต่ำกว่า 47 ปี นอนโรงพยาบาลเกิน 30 วัน มีกี่คน ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
how many patients under the age of 47 stayed in the hospital for more than 30 days?It is not neccessary to use all the tables.
 demographic:  subject_id [ text]  hadm_id [ text]  name [ text]  marital_status [ text]  age [ text]  dob [ text]  gender [ text]  language [ text]  religion [ text]  admission_type [ text]  days_stay [ text]  insurance [ text]  ethnicity [ text]  expire_flag [ text]  admission_location [ text]  discharge_location [ text]  diagnosis [ text]  dod [ text]  dob_year [ text]  dod_year [ text]  admittime [ text]  dischtime [ text]  admityear [ text] 
SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic WHERE demographic.age < "47" AND demographic.days_stay > "30"