what is the monthly minimum phosphate value for patient 9151 until 3 years ago?
select min(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 9151 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'phosphate' ) and datetime(labevents.charttime) <= datetime(current_time,'-3 year') group by strftime('%y-%m',labevents.charttime)