code: func (b *builtinRoundDecSig) evalDecimal(row chunk.Row) (*types.MyDecimal, bool, error) {
  	val, isNull, err := b.args[0].EvalDecimal(b.ctx, row)
  	if isNull || err != nil {
  		return nil, isNull, err
  	}
  	to := new(types.MyDecimal)
  	if err = val.Round(to, 0, types.ModeHalfEven); err != nil {
  		return nil, true, err
  	}
  	return to, false, nil
  }
docs: // evalDecimal evals ROUND(value).
  // See https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_round