คำนวณจำนวนคนที่เคยทำขั้นตอนเดียวตั้งแต่ 6 ปีที่แล้ว ไม่จำเป็นต้องใช้ทุกตาราง
calculate the number of people who have had procedure-one vessel since 6 years ago.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 admissions.subject_id) FROM admissions WHERE admissions.hadm_id IN (SELECT procedures_icd.hadm_id FROM procedures_icd WHERE procedures_icd.icd9_code = (SELECT d_icd_procedures.icd9_code FROM d_icd_procedures WHERE d_icd_procedures.short_title = 'procedure-one vessel') AND DATETIME(procedures_icd.charttime) >= DATETIME(CURRENT_TIME(), '-6 year'))