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

c[i + j] = inverted
                    ? Op::template apply<UInt8>(a[i + j], b_repeated[b_offset + j])
                    : Op::template apply<UInt8>(b_repeated[b_offset + j], a[i + j]);
            b_offset += b_increment;
            if (b_offset >= N) 
                b_offset -= N;
        }
    }
};
template <typename A, typename B, typename Op, typename ResultType = typename Op::ResultType>
struct BinaryOperationImpl : BinaryOperation<A, B, Op, ResultType> { };
/**
 * Binary operations with Decimals (either Decimal OP Decimal or Decimal Op Float) need to scale the args correctly.
 *  - + (plus), - (minus), * (multiply), least and greatest operations scale one of the args (which scale factor is not 1).
 *    The resulting scale is either left or the right scale.
 *  - / (divide) operation scales the first argument.
 *    The resulting scale is the first one's.
 */
template <template <typename, typename> typename Operation, class OpResultType, bool check_overflow = true>
struct DecimalBinaryOperation
{
private:
    using ResultType = OpResultType; 
    using NativeResultType = typename NativeType<ResultType>::Type; 
    using ResultContainerType = typename std::conditional_t<IsDecimalNumber<ResultType>,
        ColumnDecimal<ResultType>,
        ColumnVector<ResultType>>::Container;
public:
    template <OpCase op_case, bool is_decimal_a, bool is_decimal_b, class A, class B>
    static void NO_INLINE process(const A & a, const B & b, ResultContainerType & c,