มีคนไข้กี่คนที่ได้รับการถอนฟันตั้งแต่สองครั้งขึ้นไปจนถึงปี 2103?ไม่จำเป็นต้องใช้ตารางทั้งหมด
how many patients got tooth extraction nec two or more times until 2103?It is not neccessary to use all the tables.
 d_items:  row_id [ number]  itemid [ number]  label [ text]  linksto [ text] 
SELECT COUNT(DISTINCT t1.subject_id) FROM (SELECT admissions.subject_id, COUNT(*) AS c1 FROM procedures_icd JOIN admissions ON procedures_icd.hadm_id = admissions.hadm_id WHERE procedures_icd.icd9_code = (SELECT d_icd_procedures.icd9_code FROM d_icd_procedures WHERE d_icd_procedures.short_title = 'tooth extraction nec') AND STRFTIME('%y', procedures_icd.charttime) <= '2103' GROUP BY admissions.subject_id) AS t1 WHERE t1.c1 >= 2