Oracle join 2 tables on same column
<p>Can someone explain to me why the below query is returning null in the description field</p>

<pre><code>Table A:

OCD CCD 
A   B
C   D
E   F

Table B:
CD   DESCRIP
A    AL
B    BL
C    CL
D    DL
E    EL
F    FL

Result:
OCD  DESCRIP CCD DESCRIP
A    AL      B   BL
C    CL      D   DL
E    EL      F   FL
</code></pre>

<p>Incorrect Query:although this query runs correctly. It doesn't give description values.</p>

<pre><code>select a.ocd,b.DESCRIP,a.CCD,b.DESCRIP
from A a, B b
where a.ocd=b.cd(+)
and a.ccd=b.cd(+);
</code></pre>

<p>Correct query</p>

<pre><code>select a.ocd,b.DESCRIP,a.CCD,b.DESCRIP
from A a, B b1, B b2
where a.ocd=b1.cd(+)
and a.ccd=b2.cd(+);
</code></pre>