protected function createSelect($config = null)
	{
		$config = $config ? $config : $this->config;
		$select = array();
		if( ($columns = $config["columns"]) )
		{
			foreach($columns as $db_key => $export_key)
			{
				$select[]= "{$db_key} as {$export_key}";
			}
		}
		return $select;
	}