
select toDateTime64(-86400 ,9,'UTC') ==  1969-12-31 00:00:00.000000000

select toDateTime64(-86400.00 ,9,'UTC') ==  1970-01-01 00:00:00.000000000 


However, I expect both outputs to be same. 

Version affected : 22.8
WhichDataType which(from_type_index);
        bool can_apply_accurate_cast = (cast_type == CastType::accurate || cast_type == CastType::accurateOrNull)
            && (which.isInt() || which.isUInt() || which.isFloat());
        if (requested_result_is_nullable && checkAndGetDataType<DataTypeString>(from_type.get()))
        {
            
            
            FunctionPtr function = FunctionConvertFromString<ToDataType, FunctionName, ConvertFromStringExceptionMode::Null>::create();
            return createFunctionAdaptor(function, from_type);
        }
        else if (!can_apply_accurate_cast)
        {
            FunctionPtr function = FunctionTo<ToDataType>::Type::create();
            return createFunctionAdaptor(function, from_type);
        }
        auto wrapper_cast_type = cast_type;
        return [wrapper_cast_type, from_type_index, to_type]
            (ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, const ColumnNullable *column_nullable, size_t input_rows_count)
        {
            ColumnPtr result_column;
            auto res = callOnIndexAndDataType<ToDataType>(from_type_index, [&](const auto & types) -> bool {
                using Types = std::decay_t<decltype(types)>;
                using LeftDataType = typename Types::LeftType;
                using RightDataType = typename Types::RightType;
                if constexpr (IsDataTypeNumber<LeftDataType> && IsDataTypeNumber<RightDataType>)
                {
                    if (wrapper_cast_type == CastType::accurate)
                    {
                        result_column = ConvertImpl<LeftDataType, RightDataType, FunctionName>::execute(
                            arguments, result_type, input_rows_count, AccurateConvertStrategyAdditions());