what were the top five most frequently performed lab tests among patients aged 40s since 3 years ago?
select d_labitems.label from d_labitems where d_labitems.itemid in ( select t1.itemid from ( select labevents.itemid, dense_rank() over ( order by count(*) desc ) as c1 from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.age between 40 and 49 ) and datetime(labevents.charttime) >= datetime(current_time,'-3 year') group by labevents.itemid ) as t1 where t1.c1 <= 5 )