since 11 months ago, what was the maximum potassium value for patient 47460?
select max(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 47460 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'potassium' ) and datetime(labevents.charttime) >= datetime(current_time,'-11 month')