这句SQL对不对？

select b.qdm,
b.updtime,
isnull(b.interval,0) as iInterval,
isnull(b.ave100je,0) as saj
from shhq..shtoday a ,shapp..shday b
where a.updtime =
(select max(c.updtime) from shhq..shtoday c where c.qdm=a.qdm)
and a.qdm=b.qdm
and b.updtime=(select max(c.updtime) from shapp..shday c where c.qdm=b.qdm)
order by a.qdm