That second sql looks funny:

select det_number 
from podetail a, poheader b
where
        det_ccode=?
  and head_date > '2002/01/01'
  and det_number=?
[download]

I don't see where the join between podetail and poheader take place. I think you're ending up with a cartesian product. How do podetail and poheader relate (besides, and I assume here, podetail.det_number and poheader.head_number).

-derby