what is the four most frequent specimen test that was taken since 1 year ago?
select t1.spec_type_desc from ( select microbiologyevents.spec_type_desc, dense_rank() over ( order by count(*) desc ) as c1 from microbiologyevents where datetime(microbiologyevents.charttime) >= datetime(current_time,'-1 year') group by microbiologyevents.spec_type_desc ) as t1 where t1.c1 <= 4