code: def _get_select_columns(self, columns=None):
          
          if columns == ['*'] or columns is None:
              columns = ['%s.*' % self._related.get_table()]
  
          return columns + self._get_aliased_pivot_columns()
docs: Set the select clause for the relation query.
  
          :param columns: The columns
          :type columns: list
  
          :rtype: list