title: Postgres groupBy not working with Laravel Backpack
body: <p>I am using Laravel Backpack with Postgres. I am wanting to groupBy (or distinct?) by a column to limit the list view. I have a single table that I want to groupBy <code>thread_id</code>. My latest attempt has been something like this:</p>
  <pre><code>$this-&gt;crud-&gt;groupBy('thread_id'); 
  </code></pre>
  <p>That code returns the error:</p>
  <pre><code>message: &quot;SQLSTATE[42803]: Grouping error: 7 ERROR:  column &quot;messages.created_at&quot; must appear in the GROUP BY clause or be used in an aggregate function       
  (SQL: select count(*) as aggregate from &quot;messages&quot; where &quot;to_user_id&quot; = 2 or &quot;from_user_id&quot; = 2 group by &quot;thread_id&quot; order by &quot;thread_id&quot; desc, &quot;created_at&quot; desc)&quot;
  </code></pre>
  <p>Has anyone ran into this issue, specifically with Backpack?</p>