Symfony Native Query - symfony

Question

I work on a project under symfony, when I want to calculate the average product by month and year (date) and as doctrine doesn't include the Month or YEAR functions I used native sql but it didn't show the results, it return empty array.
If someone can help me,Thank you.
Repository:`
public function MonthEfficience()
{
$rsm = new ResultSetMappingBuilder($this->getEntityManager());
$rsm->addRootEntityFromClassMetadata('GP\PlatformBundle\Entity\Efficience', 'e');
$rsm->addJoinedEntityFromClassMetadata('GP\PlatformBundle\Entity\collectif', 'c', 'e', 'collectif', array('id' => 'collectif_id'));
$sql = 'SELECT (AVG(e.produit_real/e.produit_plan)*100) as moyenne,
MONTH(e.date) as mois, YEAR(e.date) as annee FROM efficience e, collectif c
where e.collectif_id=c.id group by mois, annee';
$query = $this->_em->createNativeQuery($sql, $rsm);
$resultats = $query->getResult();
return $resultats;
}
Controller:
public function effmonthAction()
{
$em = $this->getDoctrine()->getManager()
->getRepository('GPPlatformBundle:Efficience');
$efficiences = $em->MonthEfficience();
return $this->render('GPPlatformBundle:App:effmonth.html.twig',
array('efficiences'=>$efficiences));
}
Twig :
<table id="example" class="display" cellspacing="0" width="100%">
<thead>
<tr>
<th>Annee</th>
<th>Mois</th>
<th>Moyenne</th>
</tr>
</thead>
<tbody>
{% for efficiences in efficiences %}
<tr>
<td>{{ efficiences.produitplan }}</td>
<td>{{ efficiences.produitreal }}</td>
<td>{{ efficiences.produitplan }}</td>
</tr>
{% endfor %}
</tbody>
</table>
Resultats:
empty array