Can a table column be written to treat two different values as the same value? The title is a bit generic, but the specific issue is that the United Kingdom of Great Britain and Northern Ireland has two commonly used 2-character codes. ISO 3166-1 specifies the code GB as the proper code, but many people still use UK for that country.

Creating a separate table to store alternate country codes and updating all my queries against the main table to also perform a secondary lookup on the alternate codes table seems like overkill for a single country. At this time, I only know of that one country where this may be a problem - at least with Alpha-2 country codes.

So what I'm wondering, is if there is a way to construct a table or column such that querying a single nchar(2) column with either UK or GB will return the same record?

I know how to write individual queries to do this, but that means updating many queries in many places (stored procedures, views, UDFs, and even application code outside the database). I'm almost wondering if I can code a custom collation, inheriting from an existing collation and just add something to make the two character sequences equal to each other..?
This isn't a perfect solution but may work for you.  

Rename your source table.

EXEC sp_rename 'countries','countries_source'


Then put a view on top of it

CREATE VIEW countries AS
SELECT fields, 
    CASE WHEN CountryCode = 'GB' THEN 'UK' ELSE CountryCode END AS CountryCode
FROM countries_source


Your existing SELECT queries won't have any problems.  I think you will have to modify your UPDATE queries and might have to update your INSERT and DELETE queries as well.  But some quick tests should let you know if that's the case.