title: add any default field on select laravel eloquent
body: <p>How I can added default field on query as</p>
  
  <pre><code>SELECT "default_value" as _my_special_virtual_field FROM ...
  </code></pre>
  
  <p>this method does not work as I expect</p>
  
  <pre><code>-&gt;addSelect(['"default_value" as _my_special_virtual_field'])
  </code></pre>