what is the daily average amount of rbc, pleural patient 15794 has on the current hospital visit?
select avg(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 15794 and admissions.dischtime is null ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'rbc, pleural' ) group by strftime('%y-%m-%d',labevents.charttime)