translation from `sum` ast node to tipb::expr has incorrect field type

Bug Report

Please answer these questions before submitting your issue. Thanks!

Current transformation from sum aggregation ast node to tipb::expr has some incorrect behaviors.

1. output type must be unsigned
2. output value must not be null, however sum(null) should be null

And the cause might lies in Aggregation::toTiPBExecutor in dbms/src/Debug/astToExecutor.cpp:

        if (agg_sig == tipb::ExprType::Count || agg_sig == tipb::ExprType::Sum)
        {
            auto * ft = agg_func->mutable_field_type();
            ft->set_tp(TiDB::TypeLongLong);
            ft->set_flag(TiDB::ColumnFlagUnsigned | TiDB::ColumnFlagNotNull);
        }

1. Minimal reproduce step (Required)

By writing a simple test like

TEST_F(JoinExecutorTestRunner, agg)
try
{
    context.addMockTable("tmp", "t", {{"a", TiDB::TP::TypeLong}}, {toNullableVec<Int32>({1, {}})});
    auto request = context.scan("tmp", "t")
        .aggregation({Sum(col("a"))}, {col("a")})
        .build(context);

    {
        ASSERT_COLUMNS_EQ_R(createColumns({toNullableVec<Int64>({1, {}}), toNullableVec<Int64>({1, {}})}), executeStreams(request));
    }
}

And execute ./gtests_dbms --gtest_filter="JoinExecutorTestRunner.agg"

2. What did you expect to see? (Required)

Test passed.

3. What did you see instead (Required)

Code: 349. DB::Exception: Cannot convert NULL value to non-Nullable type

Stack trace:

     0x110988410        StackTrace::StackTrace() [gtests_dbms+4494296080]
                        dbms/src/Common/StackTrace.cpp:23
     0x11098844c        StackTrace::StackTrace() [gtests_dbms+4494296140]
                        dbms/src/Common/StackTrace.cpp:22
     0x104b788c8        DB::Exception::Exception(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, int) [gtests_dbms+4295002312]
                        dbms/src/Common/Exception.h:41
     0x104b77a20        DB::Exception::Exception(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, int) [gtests_dbms+4294998560]
                        dbms/src/Common/Exception.h:43
     0x1073fadcc        DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)::operator()(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long) const [gtests_dbms+4337479116]
                        dbms/src/Functions/FunctionsConversion.h:2884
     0x1073fabb4        decltype(std::__1::forward<DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)&>(fp)(std::__1::forward<DB::Block&>(fp0), std::__1::forward<std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&>(fp0), std::__1::forward<unsigned long>(fp0))) std::__1::__invoke<DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)&, DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long>(DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)&, DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long&&) [gtests_dbms+4337478580]
                        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/type_traits:3694
     0x1073fab24        void std::__1::__invoke_void_return_wrapper<void, true>::__call<DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)&, DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long>(DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)&, DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long&&) [gtests_dbms+4337478436]
                        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/__functional_base:348
     0x1073faabc        std::__1::__function::__alloc_func<DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long), std::__1::allocator<DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)>, void (DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)>::operator()(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long&&) [gtests_dbms+4337478332]
                        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/functional:1558
     0x1073f9650        std::__1::__function::__func<DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long), std::__1::allocator<DB::FunctionCast::prepare(std::__1::shared_ptr<DB::IDataType const> const&, std::__1::shared_ptr<DB::IDataType const> const&) const::'lambda1'(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)>, void (DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)>::operator()(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long&&) [gtests_dbms+4337473104]
                        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/functional:1732
     0x10739027c        std::__1::__function::__value_func<void (DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)>::operator()(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long&&) const [gtests_dbms+4337042044]
                        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/functional:1885
     0x10738f004        std::__1::function<void (DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long)>::operator()(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long) const [gtests_dbms+4337037316]
                        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/functional:2560
     0x10738e908        DB::ExecutableFunctionCast::executeImpl(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long) const [gtests_dbms+4337035528]
                        dbms/src/Functions/FunctionsConversion.h:2491
     0x10f63fb58        DB::IExecutableFunction::execute(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long) const [gtests_dbms+4474075992]
                        dbms/src/Functions/IFunction.cpp:230
     0x105c9c8ac        DB::IFunctionBase::execute(DB::Block&, std::__1::vector<unsigned long, std::__1::allocator<unsigned long> > const&, unsigned long) const [gtests_dbms+4312975532]
                        dbms/src/Functions/IFunction.h:98
     0x10e5817e8        DB::ExpressionAction::execute(DB::Block&) const [gtests_dbms+4456519656]
                        dbms/src/Interpreters/ExpressionActions.cpp:336
     0x10e585784        DB::ExpressionActions::execute(DB::Block&) const [gtests_dbms+4456535940]
                        dbms/src/Interpreters/ExpressionActions.cpp:662
     0x10d319b54        DB::ExpressionBlockInputStream::readImpl() [gtests_dbms+4437220180]
                        dbms/src/DataStreams/ExpressionBlockInputStream.cpp:53
     0x10d3665a4        DB::IProfilingBlockInputStream::read(DB::PODArray<unsigned char, 4096ul, Allocator<false>, 15ul, 16ul>*&, bool) [gtests_dbms+4437534116]
                        dbms/src/DataStreams/IProfilingBlockInputStream.cpp:75
     0x10d366410        DB::IProfilingBlockInputStream::read() [gtests_dbms+4437533712]
                        dbms/src/DataStreams/IProfilingBlockInputStream.cpp:43
     0x10d319af4        DB::ExpressionBlockInputStream::readImpl() [gtests_dbms+4437220084]
                        dbms/src/DataStreams/ExpressionBlockInputStream.cpp:50
     0x10d3665a4        DB::IProfilingBlockInputStream::read(DB::PODArray<unsigned char, 4096ul, Allocator<false>, 15ul, 16ul>*&, bool) [gtests_dbms+4437534116]
                        dbms/src/DataStreams/IProfilingBlockInputStream.cpp:75
     0x10d366410        DB::IProfilingBlockInputStream::read() [gtests_dbms+4437533712]
                        dbms/src/DataStreams/IProfilingBlockInputStream.cpp:43
     0x106a35318        DB::tests::(anonymous namespace)::readBlock(std::__1::shared_ptr<DB::IBlockInputStream>) [gtests_dbms+4327232280]
                        dbms/src/TestUtils/ExecutorTestUtils.cpp:111
     0x106a351e4        DB::tests::ExecutorTest::executeStreams(std::__1::shared_ptr<tipb::DAGRequest> const&, std::__1::unordered_map<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::vector<DB::ColumnWithTypeAndName, std::__1::allocator<DB::ColumnWithTypeAndName> >, std::__1::hash<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::equal_to<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::allocator<std::__1::pair<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const, std::__1::vector<DB::ColumnWithTypeAndName, std::__1::allocator<DB::ColumnWithTypeAndName> > > > >&, unsigned long) [gtests_dbms+4327231972]
                        dbms/src/TestUtils/ExecutorTestUtils.cpp:127
     0x106a354c0        DB::tests::ExecutorTest::executeStreams(std::__1::shared_ptr<tipb::DAGRequest> const&, unsigned long) [gtests_dbms+4327232704]
                        dbms/src/TestUtils/ExecutorTestUtils.cpp:132
     0x104e898a0        DB::tests::JoinExecutorTestRunner_agg_Test::TestBody() [gtests_dbms+4298217632]
                        dbms/src/Flash/tests/gtest_join_executor.cpp:370
     0x10c719db8        void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) [gtests_dbms+4424637880]
                        contrib/googletest/googletest/src/gtest.cc:2401
     0x10c6f27f8        void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) [gtests_dbms+4424476664]
                        contrib/googletest/googletest/src/gtest.cc:2437
     0x10c6f2754        testing::Test::Run() [gtests_dbms+4424476500]
                        contrib/googletest/googletest/src/gtest.cc:2473
     0x10c6f358c        testing::TestInfo::Run() [gtests_dbms+4424480140]
                        contrib/googletest/googletest/src/gtest.cc:2655
     0x10c6f4284        testing::TestCase::Run() [gtests_dbms+4424483460]
                        contrib/googletest/googletest/src/gtest.cc:2773
     0x10c6fad3c        testing::internal::UnitTestImpl::RunAllTests() [gtests_dbms+4424510780]
                        contrib/googletest/googletest/src/gtest.cc:4673
unknown file: Failure
C++ exception with description "DB::Exception" thrown in the test body.
[  FAILED  ] JoinExecutorTestRunner.agg (921 ms)
[----------] 1 test from JoinExecutorTestRunner (921 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (924 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] JoinExecutorTestRunner.agg

 1 FAILED TEST

4. What is your TiFlash version? (Required)

master

Start in dbms/src/Debug/astToExecutor.cpp at Aggregation::toTiPBExecutor, then review the JoinExecutorTestRunner.agg case in dbms/src/Flash/tests/gtest_join_executor.cpp. Run ./gtests_dbms --gtest_filter="JoinExecutorTestRunner.agg" and verify SUM output uses the intended unsigned field type while preserving NULL for SUM(NULL) without conversion errors.