Fix the issue that comparison function could not handle decimal arguments with different scale

Author: zanmato1984

cpp/src/arrow/compute/expression_test.cc

@@ -648,6 +648,10 @@ TEST(Expression, BindWithDecimalArithmeticOps) {
 }
 
 TEST(Expression, BindWithImplicitCasts) {
+  auto exciting_schema = schema(
+      {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")),
@@ -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
+    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);
+
+    // 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);
   }
 
   compute::SetLookupOptions in_a{ArrayFromJSON(utf8(), R"(["a"])")};

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

@@ -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),
+                              /*init=*/nullptr, DecimalsHaveSameScale()));
   }
 
   {