title: select union in zf2 query
body: <p>I am moving my web application from zf1 to zf2 and among the problems I have with sql queries, I can't figure out how to make a union.</p>
  
  <p>I used to be able to make </p>
  
  <pre><code>$select-&gt;union($select1, $select2, $select3) 
  </code></pre>
  
  <p>but the Zend\Db\Sql\Select does not have an <code>union()</code> method anymore.</p>
  
  <p>Is there still a way to make an union in a query with zf2?</p>