what is patient 71559's monthly minimum glucose level until 03/2103?
select min(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 71559 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'glucose' ) and strftime('%y-%m',labevents.charttime) <= '2103-03' group by strftime('%y-%m',labevents.charttime)