code: def _query_iterator(self, result, chunksize, columns, coerce_float=True,
                          parse_dates=None):
          
  
          while True:
              data = result.fetchmany(chunksize)
              if not data:
                  break
              else:
                  self.frame = DataFrame.from_records(
                      data, columns=columns, coerce_float=coerce_float)
  
                  self._harmonize_columns(parse_dates=parse_dates)
  
                  if self.index is not None:
                      self.frame.set_index(self.index, inplace=True)
  
                  yield self.frame
docs: Return generator through chunked result set.