code: private boolean retrieveOnlyRowIds(String rowIdName)
      {
          return columnHandles.isEmpty() || (columnHandles.size() == 1 && columnHandles.get(0).getName().equals(rowIdName));
      }
docs: Gets a Boolean value indicating whether or not the scanner should only return row IDs.
  <p>
  This can occur in cases such as SELECT COUNT(*) or the table only has one column.
  Presto doesn't need the entire contents of the row to count them,
  so we can configure Accumulo to only give us the first key/value pair in the row
  
  @param rowIdName Row ID column name
  @return True if scanner should retriev eonly row IDs, false otherwise