Wierd stuff

Hi 

I'm developing a system with a large number of tables.

One of the tables has (among others) the following fields:
Table    = aluno
+----------------------------------+---------------------------------
|              Field               |              Type                
+----------------------------------+---------------------------------
| numero_aluno                     | int4                             
| freguesia_naturalidade           | int2                             
| concelho_naturalidade            | int2                             
| nacionalidade                    | int2                             

another is like this:


-- Table    = concelho
+----------------------------------+---------------------------------
|              Field               |              Type                
+----------------------------------+---------------------------------
| codigo                           | int4                             
| nome                             | text                             

The field "concelho_naturalidade" on the first table has values taken
from the "codigo" field from the second.

Now comes the problem:

When i do :
sac=> select a.numero_aluno, a.concelho_naturalidade from aluno a where
a.numero_aluno=13792;

i get:

numero_aluno|concelho_naturalidade
------------+---------------------
       13792|                 1006
(1 row)

and whith:
sac=> select * from concelho where codigo=1006;

i get:

codigo|nome            
------+----------------
  1006|CALDAS DA RAINHA
(1 row)

but with:
sac=> select c.nome from aluno a, concelho c where
a.concelho_naturalidade=c.codigo and a.numero_aluno=13792;

i get:

nome
----
(0 rows)

If my SQL is worth anything I thought it would reply "Caldas da Rainha".
What is wrong here?

I'm using POstgresql 6.3.2 (yes i know: I should upgrade)

Thanks

--
        Mario Filipe 
        mjnf@uevora.pt
        http://neptuno.sc.uevora.pt/~mjnf