ลองอันนี้ครับ...สด ๆ เดี๋ยวนี้เลย
select distinct pt.hn, concat(pt.pname,pt.fname," ",pt.lname) as pt_name
from ovstdiag odx
join vn_stat v on v.vn=odx.vn
join patient pt on pt.hn=v.hn
where (v.age_y>= 0 and v.age_y <= 200) and (odx.icd10 between "B20" and "B24") and (v.vstdate between "2010-01-01" and "2010-01-31")
order by pt.hn