/**
* Returns the unique element IDs that match a given element query.
*
* @param DbCommand $query
* @return array
*/
private function _getElementIdsFromQuery(DbCommand $query)
{
// Get the matched element IDs, and then have the SearchService filter them.
$elementIdsQuery = craft()->db->createCommand()->select('elements.id')->from('elements elements')->group('elements.id');
$elementIdsQuery->setWhere($query->getWhere());
$elementIdsQuery->setJoin($query->getJoin());
$elementIdsQuery->params = $query->params;
return $elementIdsQuery->queryColumn();
}