这确实有点模糊。下面是做算术十进制类型转换的相关代码。

/**
   * Returns the result type for (t1 op t2) where t1 and t2 are both DECIMAL, used when
   * DECIMAL version 2 is enabled.
   *
   * These rules are similar to (post Dec 2016) Hive / sql server rules.
   * http://blogs.msdn.com/b/sqlprogrammability/archive/2006/03/29/564110.aspx
   * https://msdn.microsoft.com/en-us/library/ms190476.aspx
   *
   * TODO: implement V2 rules for ADD/SUB.
   *
   * Changes:
   *  - There are slight difference with how precision/scale reduction occurs compared
   *    to SQL server when the desired precision is more than the maximum supported
   *    precision.  But an algorithm of reducing scale to a minimum of 6 is used.
   */
  private static ScalarType getDecimalArithmeticResultTypeV2(Type t1, Type t2,
      ArithmeticExpr.Operator op) throws AnalysisException {
    Preconditions.checkState(t1.isFullySpecifiedDecimal());
    Preconditions.checkState(t2.isFullySpecifiedDecimal());
    ScalarType st1 = (ScalarType) t1;
    ScalarType st2 = (ScalarType) t2;
    int s1 = st1.decimalScale();
    int s2 = st2.decimalScale();
    int p1 = st1.decimalPrecision();
    int p2 = st2.decimalPrecision();
    int resultScale;
    int resultPrecision;

    switch (op) {
      case DIVIDE:
        // Divide result always gets at least MIN_ADJUSTED_SCALE decimal places.
        resultScale = Math.max(ScalarType.MIN_ADJUSTED_SCALE, s1 + p2 + 1);
        resultPrecision = p1 - s1 + s2 + resultScale;
        break;
      case MOD:
        resultScale = Math.max(s1, s2);
        resultPrecision = Math.min(p1 - s1, p2 - s2) + resultScale;
        break;
      case MULTIPLY:
        resultScale = s1 + s2;
        resultPrecision = p1 + p2 + 1;
        break;
      case ADD:
      case SUBTRACT:
      default:
        // Not yet implemented - fall back to V1 rules.
        return getDecimalArithmeticResultTypeV1(t1, t2, op);
    }
    // Use the scale reduction technique when resultPrecision is too large.
    return ScalarType.createAdjustedDecimalType(resultPrecision, resultScale);
  }

因此，5.30001为精度6和比例尺5，2342.1为精度5和比例尺1。我们有s1=5和p2=5。输出刻度为s1+p2+1==11，精度为6-5+1+11==13。在评论链接中可以更好地解释这些规则。