instruction: what is the monthly minimum lactate dehydrogenase (ld) level of patient 14397 since 03/2104?
response: SELECT MIN(labevents.valuenum) FROM labevents WHERE labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 14397) AND labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'lactate dehydrogenase (ld)') AND STRFTIME('%y-%m', labevents.charttime) >= '2104-03' GROUP BY STRFTIME('%y-%m', labevents.charttime)