the-biergarten-app/archive/sql-stored-procs-functions/02-functions/UDF_GetCountryIdByCode.sql

CREATE OR ALTER FUNCTION dbo.UDF_GetCountryIdByCode(
    @CountryCode NVARCHAR(2)
)
    RETURNS UNIQUEIDENTIFIER
AS
BEGIN
    DECLARE
        @CountryId UNIQUEIDENTIFIER;

    SELECT @CountryId = CountryID
    FROM dbo.Country
    WHERE ISO3166_1 = @CountryCode;

    RETURN @CountryId;
END;