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

if constexpr (std::is_same_v<DataTypeFixedString, LeftDataType> ||
                          std::is_same_v<DataTypeFixedString, RightDataType>)
            {
                if constexpr (!Op<DataTypeFixedString, DataTypeFixedString>::allow_fixed_string)
                    return false;
                else if constexpr (std::is_same_v<LeftDataType, RightDataType>)
                {
                    if (left.getN() == right.getN())
                    {
                        type_res = std::make_shared<LeftDataType>(left.getN());
                        return true;
                    }
                }
            }
            else
            {
                using ResultDataType = typename BinaryOperationTraits<Op, LeftDataType, RightDataType>::ResultDataType;
                if constexpr (!std::is_same_v<ResultDataType, InvalidType>)
                {
                    if constexpr (IsDataTypeDecimal<LeftDataType> && IsDataTypeDecimal<RightDataType>)
                    {
                        ResultDataType result_type = decimalResultType<is_multiply, is_division>(left, right);
                        type_res = std::make_shared<ResultDataType>(result_type.getPrecision(), result_type.getScale());
                    }
                    else if constexpr ((IsDataTypeDecimal<LeftDataType> && IsFloatingPoint<RightDataType>) ||
                        (IsDataTypeDecimal<RightDataType> && IsFloatingPoint<LeftDataType>))
                        type_res = std::make_shared<std::conditional_t<IsFloatingPoint<LeftDataType>,
                            LeftDataType, RightDataType>>();
                    else if constexpr (IsDataTypeDecimal<LeftDataType>)
                        type_res = std::make_shared<LeftDataType>(left.getPrecision(), left.getScale());