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GH-41011: [C++][Compute] Fix the issue that comparison function could not handle decimal arguments with different scales #47459

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Merged
zanmato1984 merged 4 commits into from
Sep 4, 2025
Merged

GH-41011: [C++][Compute] Fix the issue that comparison function could not handle decimal arguments with different scales #47459

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62eab1d
Fix the issue that comparison function could not handle decimal argum…
zanmato1984 Aug 29, 2025
d3aee89
Merge remote-tracking branch 'apache/main' into fix/gh-41011
zanmato1984 Sep 3, 2025
f2c4c91
Update cpp/src/arrow/compute/expression_test.cc
zanmato1984 Sep 3, 2025
530b929
Address comment: add cases for different precisions same scale
zanmato1984 Sep 3, 2025
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40 changes: 40 additions & 0 deletions cpp/src/arrow/compute/expression_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -648,6 +648,10 @@ TEST(Expression, BindWithDecimalArithmeticOps) {
}

TEST(Expression, BindWithImplicitCasts) {
auto exciting_schema = schema(
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@zanmato1984 zanmato1984 Sep 3, 2025

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Get excited one more time! @pitrou

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@pitrou pitrou Sep 3, 2025

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My head spins.

{field("i64", int64()), field("dec128_3_2", decimal128(3, 2)),
field("dec128_5_3", decimal128(5, 3)), field("dec256_3_2", decimal256(3, 2)),
field("dec256_5_3", decimal256(5, 3))});
for (auto cmp : {equal, not_equal, less, less_equal, greater, greater_equal}) {
// cast arguments to common numeric type
ExpectBindsTo(cmp(field_ref("i64"), field_ref("i32")),
Expand Down Expand Up @@ -708,6 +712,42 @@ TEST(Expression, BindWithImplicitCasts) {
ExpectBindsTo(cmp(field_ref("i32"), literal(std::make_shared<DoubleScalar>(10.0))),
cmp(cast(field_ref("i32"), float32()),
literal(std::make_shared<FloatScalar>(10.0f))));

// decimal int
ExpectBindsTo(cmp(field_ref("dec128_3_2"), field_ref("i64")),
cmp(field_ref("dec128_3_2"), cast(field_ref("i64"), decimal128(21, 2))),
/*bound_out=*/nullptr, *exciting_schema);
ExpectBindsTo(cmp(field_ref("i64"), field_ref("dec128_3_2")),
cmp(cast(field_ref("i64"), decimal128(21, 2)), field_ref("dec128_3_2")),
/*bound_out=*/nullptr, *exciting_schema);

// decimal128 decimal256 with different scales
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@pitrou pitrou Sep 3, 2025

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What happens with the same scale and different precisions, btw? Ideally no cast would occur since the raw values can be compared directly, but regardless we might add tests for that situation as well?

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@zanmato1984 zanmato1984 Sep 3, 2025

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You are right, no casts applied for different precisions but same scale.

Added the cases. Thank you!

ExpectBindsTo(
cmp(field_ref("dec128_3_2"), field_ref("dec256_5_3")),
cmp(cast(field_ref("dec128_3_2"), decimal256(4, 3)), field_ref("dec256_5_3")),
/*bound_out=*/nullptr, *exciting_schema);
ExpectBindsTo(
cmp(field_ref("dec256_5_3"), field_ref("dec128_3_2")),
cmp(field_ref("dec256_5_3"), cast(field_ref("dec128_3_2"), decimal256(4, 3))),
/*bound_out=*/nullptr, *exciting_schema);
ExpectBindsTo(cmp(field_ref("dec128_5_3"), field_ref("dec256_3_2")),
cmp(cast(field_ref("dec128_5_3"), decimal256(5, 3)),
cast(field_ref("dec256_3_2"), decimal256(4, 3))),
/*bound_out=*/nullptr, *exciting_schema);
ExpectBindsTo(cmp(field_ref("dec256_3_2"), field_ref("dec128_5_3")),
cmp(cast(field_ref("dec256_3_2"), decimal256(4, 3)),
cast(field_ref("dec128_5_3"), decimal256(5, 3))),
/*bound_out=*/nullptr, *exciting_schema);
Comment on lines +716 to +851
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@zanmato1984 zanmato1984 Aug 29, 2025

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These cases will actually pass w/o this fix. Just added them for intact coverage of all decimal casting paths.


// decimal decimal with different scales
ExpectBindsTo(
cmp(field_ref("dec128_3_2"), field_ref("dec128_5_3")),
cmp(cast(field_ref("dec128_3_2"), decimal128(4, 3)), field_ref("dec128_5_3")),
/*bound_out=*/nullptr, *exciting_schema);
ExpectBindsTo(
cmp(field_ref("dec128_5_3"), field_ref("dec128_3_2")),
cmp(field_ref("dec128_5_3"), cast(field_ref("dec128_3_2"), decimal128(4, 3))),
/*bound_out=*/nullptr, *exciting_schema);
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@zanmato1984 zanmato1984 Aug 29, 2025

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These two will fail w/o the fix.

}

compute::SetLookupOptions in_a{ArrayFromJSON(utf8(), R"(["a"])")};
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4 changes: 2 additions & 2 deletions cpp/src/arrow/compute/kernels/scalar_compare.cc
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Expand Up @@ -436,8 +436,8 @@ std::shared_ptr<ScalarFunction> MakeCompareFunction(std::string name, FunctionDo

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)));
DCHECK_OK(func->AddKernel({InputType(id), InputType(id)}, boolean(), std::move(exec),
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@zanmato1984 zanmato1984 Aug 29, 2025 •
edited
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Yep, the fix is as simple as this. Thanks to #47297.

/*init=*/nullptr, DecimalsHaveSameScale()));
}

{
Expand Down
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