title: PDO::FETCH_COLUMN fetches nothing
body: <p>The following code gives me an array <code>$a</code> containing <code>description</code>. </p>
  
  <pre><code>$stmt = $dbh-&gt;prepare("SELECT description, id
      FROM money_items");
  $stmt-&gt;execute();
  $a = $stmt-&gt;fetchAll(PDO::FETCH_COLUMN, 0);
  $id = $stmt-&gt;fetchAll(PDO::FETCH_COLUMN, 1);
  </code></pre>
  
  <p>But the <code>$id</code> array comes out blank.</p>
  
  <pre><code>   Array
     (
     )
  </code></pre>
  
  <p>If I remove the <code>$a = $stmt-&gt;fetchAll(PDO::FETCH_COLUMN, 0);</code> line, the <code>$id</code> array comes out fine. Am I only allowed to fetch one column from the results?</p>