code: func CompareDuration(sctx sessionctx.Context, lhsArg, rhsArg Expression, lhsRow, rhsRow chunk.Row) (int64, bool, error) {
  	arg0, isNull0, err := lhsArg.EvalDuration(sctx, lhsRow)
  	if err != nil {
  		return 0, true, err
  	}
  
  	arg1, isNull1, err := rhsArg.EvalDuration(sctx, rhsRow)
  	if err != nil {
  		return 0, true, err
  	}
  
  	if isNull0 || isNull1 {
  		return compareNull(isNull0, isNull1), true, nil
  	}
  	return int64(arg0.Compare(arg1)), false, nil
  }
docs: // CompareDuration compares two durations.