oh what is the average value of chloride, whole blood on patient 45321 in 04/2103?
select avg(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 45321 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'chloride, whole blood' ) and strftime('%y-%m',labevents.charttime) = '2103-04'