instruction: what is a number of times that patient 17638 has had an l nephrostomy's output in 05/2105?
response: SELECT COUNT(*) FROM outputevents WHERE outputevents.icustay_id IN (SELECT icustays.icustay_id FROM icustays WHERE icustays.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 17638)) AND outputevents.itemid IN (SELECT d_items.itemid FROM d_items WHERE d_items.label = 'l nephrostomy' AND d_items.linksto = 'outputevents') AND STRFTIME('%y-%m', outputevents.charttime) = '2105-05'