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

template <> inline constexpr bool UseLeftDecimal<DataTypeDecimal<Decimal128>, DataTypeDecimal<Decimal64>> = true;
template <> inline constexpr bool UseLeftDecimal<DataTypeDecimal<Decimal64>, DataTypeDecimal<Decimal32>> = true;
template <template <typename, typename> class Operation, typename LeftDataType, typename RightDataType>
struct BinaryOperationTraits
{
    using T0 = typename LeftDataType::FieldType;
    using T1 = typename RightDataType::FieldType;
private: 
    using Op = Operation<T0, T1>;
public:
    static constexpr bool allow_decimal = IsOperation<Operation>::allow_decimal;
    
    
    using ResultDataType = Switch<
        
        Case<!allow_decimal && (IsDataTypeDecimal<LeftDataType> || IsDataTypeDecimal<RightDataType>), InvalidType>,
        Case<IsDataTypeDecimal<LeftDataType> && IsDataTypeDecimal<RightDataType> && UseLeftDecimal<LeftDataType, RightDataType>, LeftDataType>,
        Case<IsDataTypeDecimal<LeftDataType> && IsDataTypeDecimal<RightDataType>, RightDataType>,
        Case<IsDataTypeDecimal<LeftDataType> && IsIntegralOrExtended<RightDataType>, LeftDataType>,
        Case<IsDataTypeDecimal<RightDataType> && IsIntegralOrExtended<LeftDataType>, RightDataType>,
        
        Case<IsOperation<Operation>::multiply && IsDataTypeDecimal<LeftDataType> && IsFloatingPoint<RightDataType>,
            RightDataType>,
        Case<IsOperation<Operation>::multiply && IsDataTypeDecimal<RightDataType> && IsFloatingPoint<LeftDataType>,
            LeftDataType>,
        
        Case<IsDataTypeDecimal<LeftDataType> && !IsIntegralOrExtendedOrDecimal<RightDataType>, InvalidType>,
        Case<IsDataTypeDecimal<RightDataType> && !IsIntegralOrExtendedOrDecimal<LeftDataType>, InvalidType>,
        
        Case<!IsDateOrDateTime<LeftDataType> && !IsDateOrDateTime<RightDataType>,