what is the yearly minimum amount of lactate patient 2957 has since 4 years ago?
select min(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 2957 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'lactate' ) and datetime(labevents.charttime) >= datetime(current_time,'-4 year') group by strftime('%y',labevents.charttime)