what is patient 2004's minimum sodium, urine value until 09/2105?
select min(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 2004 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'sodium, urine' ) and strftime('%y-%m',labevents.charttime) <= '2105-09'