I've been studying basic usage and I found wrong minus result on DecimalXX type.

**Example Query**
`
select toDecimal64(4,4) - toDecimal32(2,2)
`

**Expected output**
2.0000

**Actual output**
3.9800

Is there anything wrong or maybe my misunderstanding of toDecimal ?

![image](https://user-images.githubusercontent.com/8475371/107513855-cdd57a00-6be3-11eb-841d-d425a198d172.png)


**How to reproduce**
1. OS: macOS Catalina 10.15.5
2. server: clickhouse-server, built from source, version 21.3.1.1
3. client:  clickhouse-client,  built from source, version 21.3.1.1

static constexpr bool is_compare =      IsOperation<Operation>::least ||
                                            IsOperation<Operation>::greatest;
    static constexpr bool is_plus_minus_compare = is_plus_minus || is_compare;
    static constexpr bool can_overflow = is_plus_minus || is_multiply;
    using Op = std::conditional_t<is_float_division,
        DivideIntegralImpl<NativeResultType, NativeResultType>, 
        Operation<NativeResultType, NativeResultType>>;
    template <OpCase op_case, OpCase target, class E>
    static auto unwrap(const E& elem, size_t i)
    {
        if constexpr (op_case == target)
            return undec(elem);
        else
            return undec(elem[i]);
    }
    
    static NativeResultType apply(NativeResultType a, NativeResultType b)
    {
        if constexpr (can_overflow && check_overflow)
        {
            NativeResultType res;
            if (Op::template apply<NativeResultType>(a, b, res))
                throw Exception("Decimal math overflow", ErrorCodes::DECIMAL_OVERFLOW);
            return res;
        }
        else
            return Op::template apply<NativeResultType>(a, b);
    }
    template <bool scale_left, bool may_check_overflow = true>
    static NO_SANITIZE_UNDEFINED NativeResultType applyScaled(NativeResultType a, NativeResultType b, NativeResultType scale)