เมื่อใดที่ผู้ป่วย 20033 มีค่า ph ต่ำสุดสุดท้ายจนถึง 09/2104? ไม่จำเป็นต้องใช้ตารางทั้งหมด
when did patient 20033 have the last minimum ph value until 09/2104?It is not neccessary to use all the tables.
 microbiologyevents:  row_id [ number]  subject_id [ number]  hadm_id [ number]  charttime [ time]  spec_type_desc [ text]  org_name [ text] 
SELECT labevents.charttime FROM labevents WHERE labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 20033) AND labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'ph') AND STRFTIME('%y-%m', labevents.charttime) <= '2104-09' ORDER BY labevents.valuenum, labevents.charttime DESC LIMIT 1