code: def get_field_identifiers(self):
          
          field_identifiers = []
          for table in self.tables:
              field_identifiers += table.get_field_identifiers()
          for join_item in self.joins:
              field_identifiers += join_item.right_table.get_field_identifiers()
          return field_identifiers
docs: Builds a list of the field identifiers for all tables and joined tables by calling
          ``get_field_identifiers()`` on each table
  
          :return: list of field identifiers
          :rtype: list of str