Hello again! 
Sadly my problem still exists. This query right here:

SELECT
ca.CountryName,
cb.CountryName,
SUM((case when ca.CountryName < cb.CountryName then -1 else 1 end) * CONVERT(money, (od.UnitPrice * od.Quantity) * (1 - od.Discount)...

I had some time to work on it, now I have this query:

SELECT
MAX(ca.CountryName) as CountryA,
MIN(cb.CountryName) as CountryB,
SUM((case when ca.CountryName < cb.CountryName then...