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 (left.column && isColumnConst(*left.column) && arguments.size() == 1)
        {
            ColumnsWithTypeAndName columns_with_constant
                = {{left.column->cloneResized(input_rows_count), left.type, left.name},
                   arguments[0]};
            return Base::executeImpl(columns_with_constant, result_type, input_rows_count);
        }
        else if (right.column && isColumnConst(*right.column) && arguments.size() == 1)
        {
            ColumnsWithTypeAndName columns_with_constant
                = {arguments[0],
                   {right.column->cloneResized(input_rows_count), right.type, right.name}};
            return Base::executeImpl(columns_with_constant, result_type, input_rows_count);
        }
        else
            return Base::executeImpl(arguments, result_type, input_rows_count);
    }
    bool hasInformationAboutMonotonicity() const override
    {
        const std::string_view name_view = Name::name;
        return (name_view == "minus" || name_view == "plus" || name_view == "divide" || name_view == "intDiv");
    }
    Monotonicity getMonotonicityForRange(const IDataType &, const Field & left_point, const Field & right_point) const override