title: zf2 \Zend\Db\Sql\Sql using predicate in where condition
body: <p>i really don't get the point how to use predicates in zend framework 2.</p>
  
  <p>this is what i got:</p>
  
  <pre><code>$sql-&gt;select()
          -&gt;columns(array('GroupedColum'
              ,'minValue' =&gt; new Expression('min(ValueColumn)')))
          -&gt;from('ValueTable')
          -&gt;group('GroupedColum')
          -&gt;order('minValue')
          -&gt;order('GroupedColum')
          -&gt;limit(10);
  </code></pre>
  
  <p>this is working fine</p>
  
  <p>now i want to apply somethin like that:</p>
  
  <pre><code>$predicate = new Zend\Db\Sql\Predicate\Predicate();
  $sql-&gt;where($predicate-&gt;greaterThan('filterColumn','20);
  </code></pre>
  
  <p>this is what i tried, it throws no error, but it is not working :-(</p>
  
  <p>This is what i expect as SQL:</p>
  
  <pre><code>select GroupedColum
      , min(ValueColumn) as minValue
  from ValueTable
  where filterColumn &gt; 20
  group by GroupedColum
  order by minValue
      GroupedColum
  limit 10;
  </code></pre>