$db    = JFactory::getDbo();
$query = $db->getQuery(true);
$query->select('a.id, a.name, a.username, b.group_id')
      ->from ('#__users a')
      ->join ('INNER', '#__user_usergroup_map b')
      ->where('b.group_id=10')
      ->where('a.block=0')
      ->order($order);

$db->setQuery($query);
return $db->loadObjectList();

$db   = JFactory::getDbo();
    $query = $db->getQuery(true);
    $query->select('a.id, a.name, a.username, b.group_id')
          ->from ('#__users a')
          ->join ('INNER', '#__user_usergroup_map b')
          ->where('b.group_id=10')
          ->where('a.block=0','AND')
          ->order($order);

    $db->setQuery($query);
    return $db->loadObjectList();

->innerJoin("#__user_usergroup_map b ON a.id = b.user_id")