until 03/2104, what was the average mcv value for patient 69289?
select avg(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 69289 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'mcv' ) and strftime('%y-%m',labevents.charttime) <= '2104-03'