what is the daily maximum ph value for patient 64292 until 4 months ago?
select max(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 64292 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'ph' ) and datetime(labevents.charttime) <= datetime(current_time,'-4 month') group by strftime('%y-%m-%d',labevents.charttime)