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 (is_multiply)
                    return ResultType{1};
                else
                    return type.scaleFactorFor(right, is_division);
            }
            else if constexpr (right_is_decimal)
            {
                if (col_right_const)
                    return ResultType{1};
                return 1 / DecimalUtils::convertTo<ResultType>(right.getScaleMultiplier(), 0);
            }
            else
                return 1;
        }();
        
        if (col_left_const && col_right_const)
        {
            const NativeResultType const_a = helperGetOrConvert<T0, ResultDataType>(col_left_const, left);
            const NativeResultType const_b = helperGetOrConvert<T1, ResultDataType>(col_right_const, right);
            const ResultType res = check_decimal_overflow
                
                ? OpImplCheck::template process<left_is_decimal, right_is_decimal>(const_a, const_b, 1, 1)
                : OpImpl::template process<left_is_decimal, right_is_decimal>(const_a, const_b, 1, 1);
            if constexpr (result_is_decimal)
                return ResultDataType(type.getPrecision(), type.getScale()).createColumnConst(
                    col_left_const->size(), toField(res, type.getScale()));
            else
                 return ResultDataType().createColumnConst(col_left_const->size(), toField(res));
        }