code: func (e *SortExec) keyColumnsLess(i, j int) bool {
  	rowI := e.rowChunks.GetRow(e.rowPtrs[i])
  	rowJ := e.rowChunks.GetRow(e.rowPtrs[j])
  	return e.lessRow(rowI, rowJ)
  }
docs: // keyColumnsLess is the less function for key columns.