title: Oracle Sql: foreign-key is also primary key syntax
body: <p>I just have a quick question about notation. I have two tables right now. </p>
  
  <p>This one has basic animal information:</p>
  
  <pre><code> create table d_animals (
    an_id     integer     primary key
  , an_gender varchar2(1) not null
  , an_dob    date        not null
  , an_name   varchar2(10)    not null
  );
  </code></pre>
  
  <p>This one is about cats:</p>
  
  <pre><code> create table d_cats (
         an_id                        integer     primary key
       , feline_leukemia_test_date    date        not null
       , an_id    foreign key references d_animals_(an_id)
       );
  </code></pre>
  
  <p>As you can see, I'm trying to use an_id as the primary key in d_cats but also refernce the an_id from the d_animals table.  I'm getting the following error for d_cats:</p>
  
  <pre><code> ORA-00957: duplicate column name
  </code></pre>
  
  <p>So how do I correctly write this?</p>
  
  <p>Also, I don't want to create another column for d_cats. My professor wants us to write d_cats with only an_id and feline_leukemia_test_Date. 
  Thanks. </p>