since 89 months ago, what was the daily average value of the potassium of patient 81223?
select avg(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 81223 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'potassium' ) and datetime(labevents.charttime) >= datetime(current_time,'-89 month') group by strftime('%y-%m-%d',labevents.charttime)