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_assert(is_plus_minus_compare || is_multiply);
        NativeResultType res;
        if constexpr (check_overflow && may_check_overflow)
        {
            bool overflow = false;
            if constexpr (scale_left)
                overflow |= common::mulOverflow(a, scale, a);
            else
                overflow |= common::mulOverflow(b, scale, b);
            if constexpr (can_overflow)
                overflow |= Op::template apply<NativeResultType>(a, b, res);
            else
                res = Op::template apply<NativeResultType>(a, b);
            if (overflow)
                throw Exception("Decimal math overflow", ErrorCodes::DECIMAL_OVERFLOW);
        }
        else
        {
            if constexpr (scale_left)
                a *= scale;
            else
                b *= scale;
            res = Op::template apply<NativeResultType>(a, b);
        }
        return res;
    }
    template <bool is_decimal_a>
    static NO_SANITIZE_UNDEFINED NativeResultType applyScaledDiv(NativeResultType a, NativeResultType b, NativeResultType scale)