I'm write a simple code in sonata admin with createQuery() for configureListFields(). 
When I write groupby , I get the following error: 
The query returned multiple rows. Change the query or use a different result function like
getScalarResult().
public function createQuery($context = 'list')
{
    $query = parent::createQuery($context);
    $rootAlias = $query->getRootAliases()[0];
    $query->groupby($rootAlias.'.cityId');
    return $query;
}