[C++] Decimal types array compare with different scales make error results

[ZhangHuiGui]

Describe the bug, including details regarding any error messages, version, and platform.

Our CompareFunction has it's own DispatchBest and supposed do cast with kAdd promotion rule during Bind.

arrow/cpp/src/arrow/compute/kernels/scalar_compare.cc

Lines 341 to 345 in 72d20ad

	Result<const Kernel*> DispatchBest(std::vector<TypeHolder>* types) const override {
	RETURN_NOT_OK(CheckArity(types->size()));
	if (HasDecimal(*types)) {
	RETURN_NOT_OK(CastBinaryDecimalArgs(DecimalPromotion::kAdd, types));
	}

But we haven't check the input decimal types' scale as ResolveDecimalAdditionOrSubtractionOutput does.

arrow/cpp/src/arrow/compute/kernels/scalar_compare.cc

Lines 435 to 439 in 72d20ad

	for (const auto id : {Type::DECIMAL128, Type::DECIMAL256}) {
	auto exec = GenerateDecimal<applicator::ScalarBinaryEqualTypes, BooleanType, Op>(id);
	DCHECK_OK(
	func->AddKernel({InputType(id), InputType(id)}, boolean(), std::move(exec)));
	}

So the decimal array's comparison won't be casted and it's results will wrong when input decimal's scales are same.

Component(s)

C++

[zanmato1984]

I believe #47297 did the trick in a more elegant way. I'll try fixing this by leveraging that.

[zanmato1984]

Hi @ZhangHuiGui , I see you have a PR for this issue. However I believe we have a better way to fix it using #47297. Would you consider doing that in your PR? Or do you mind if I work on a new fix? Thanks.

[ZhangHuiGui]

Would you consider doing that in your PR? Or do you mind if I work on a new fix? Thanks.

Sorry, I've been too busy recently. Your method is more elegant and you can submit a separate PR. Thank you very much!