นับจำนวนผู้ป่วยที่ได้รับการผ่าตัดเมดิแอสติโนสโคปในเดือนเดียวกันหลังจากได้รับการผ่าตัดทรวงอก ไม่จำเป็นต้องใช้ตารางทั้งหมด
count the number of patients who have received an mediastinoscopy procedure in the same month after getting a thoracentesis procedure.It is not neccessary to use all the tables.
 chartevents:  row_id [ number]  subject_id [ number]  hadm_id [ number]  icustay_id [ number]  itemid [ number]  charttime [ time]  valuenum [ number]  valueuom [ text] 
SELECT COUNT(DISTINCT t1.subject_id) FROM (SELECT admissions.subject_id, procedures_icd.charttime 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 = 'thoracentesis')) AS t1 JOIN (SELECT admissions.subject_id, procedures_icd.charttime 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 = 'mediastinoscopy')) AS t2 ON t1.subject_id = t2.subject_id WHERE t1.charttime < t2.charttime AND DATETIME(t1.charttime, 'start of month') = DATETIME(t2.charttime, 'start of month')