Custom $query->orderby did not worked

I need to sort user birth date in current month order by birth date, so i make custom order in my_module_views_query_alter(),
but seems datatables sorting is override this customization, is this normal ?

		$query->orderby = array(
		  array(
			'field' => "DATE_FORMAT(STR_TO_DATE(field_data_field_birth_date.field_birth_date_value, '%Y-%m-%dT%T'), '%m%d')",
			'direction' => 'ASC',
		  )
		);

rgds