public boolean shouldConvertDecimal64ToDecimal() {
    return getOutputDataTypePhysicalVariation() == DataTypePhysicalVariation.NONE;
  }
By default vector expressions do not handle decimal64 types and should be
converted into Decimal types if its output cannot handle Decimal64. Decimal64
that only deal with Decimal64 types cannot handle conversions so they should
override this method and return false.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/VectorExpression.java