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