Query with subquery should return value but doesn't

Question

When I run this SQL, it returns no value:
SELECT vfn.cat
FROM vps_fishery_ner vfn, valid_fishery vf
WHERE vfn.plan = vf.plan
AND vfn.cat = vf.cat
AND vf.permit_year = 2010
AND vf.moratorium_fishery = 'T'
AND vfn.vp_num = 211652
AND vfn.ap_year = 2010
AND vfn.plan = 'MUL'
AND vfn.date_issued = (SELECT MAX(date_issued)
FROM vps_fishery_ner
WHERE vp_num = 211652
AND ap_year = 2010);
In order to test, I take out the subquery and run it separately:
SELECT MAX(date_issued)
FROM vps_fishery_ner
WHERE vp_num = 211652
AND ap_year = 2010;
Returns 02-APR-10
Then I paste this date into the original query (using the TRUNC function, of course, since I hardcode only the DDMMYY part of the date):
SELECT vfn.cat
FROM vps_fishery_ner vfn, valid_fishery vf
WHERE vfn.plan = vf.plan
AND vfn.cat = vf.cat
AND vf.permit_year = 2010
AND vf.moratorium_fishery = 'T'
AND vfn.vp_num = 211652
AND vfn.ap_year = 2010
AND vfn.plan = 'MUL'
AND TRUNC(date_issued) = TO_DATE('02-APR-10');
And this returns the required value, 'A'.
So why doesn't the full query with subquery work, if the value that is returned by the subquery is valid and works when you just paste it in?
Thanks.

Answer 1

Hi,
Not sure about your question.
But you say when you uss 01-apr-10 you get the expected results.
So why dont you try using trunc on botht sides
SELECT vfn.cat
  FROM vps_fishery_ner vfn, valid_fishery vf
WHERE vfn.plan = vf.plan
   AND vfn.cat = vf.cat
   AND vf.permit_year = 2010
   AND vf.moratorium_fishery = 'T'
   AND vfn.vp_num = 211652
   AND vfn.ap_year = 2010
   AND vfn.plan = 'MUL'
   AND trunc(vfn.date_issued) = (SELECT MAX(trunc(date_issued))
                            FROM vps_fishery_ner
                           WHERE vp_num = 211652
                             AND ap_year = 2010);Rememeber if you are couting on some Index to be used you might want to recheck.
IN answer to your question why it does not return with subquery included, because the TIME PART is not the same.
You yourself proved it by using the supplying only the date part.
Regards,
Bhushan