count the number of times patient 27703's rbc, csf test has been taken last month.
select count(*) from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'rbc, csf' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 27703 ) and datetime(labevents.charttime,'start of month') = datetime(current_time,'start of month','-1 month')