ระบุจำนวนผู้ป่วยที่เข้ารับการรักษาน้อยกว่า 2,148 ปี และวินิจฉัยชื่อยาวเป็นแผลกดทับ สะโพก ไม่จำเป็นต้องใช้ทุกตาราง
provide the number of patients whose admission year is less than 2148 and diagnoses long title is pressure ulcer, buttock?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 INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id WHERE demographic.admityear < "2148" AND diagnoses.long_title = "Pressure ulcer, buttock"