/**
  * @param QOM\SelectorInterface $source
  * @param string                $alias
  *
  * @return string
  */
 private function sqlNodeTypeClause($alias, QOM\SelectorInterface $source)
 {
     $sql = "{$alias}.type IN ('" . $source->getNodeTypeName() . "'";
     $subTypes = $this->nodeTypeManager->getSubtypes($source->getNodeTypeName());
     foreach ($subTypes as $subType) {
         /* @var $subType \PHPCR\NodeType\NodeTypeInterface */
         $sql .= ", '" . $subType->getName() . "'";
     }
     $sql .= ')';
     return $sql;
 }