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 (valid_on_float_arguments)
        {
            return castType(left, [&](const auto & left_)
            {
                return castType(right, [&](const auto & right_)
                {
                    return f(left_, right_);
                });
            });
        }
        else
        {
            return castTypeNoFloats(left, [&](const auto & left_)
            {
                return castTypeNoFloats(right, [&](const auto & right_)
                {
                    return f(left_, right_);
                });
            });
        }
    }
    static FunctionOverloadResolverPtr