UFN_LETTERCODE_GETLETTERNAME

create function dbo.UFN_LETTERCODE_GETLETTERNAME(@ID uniqueidentifier)
returns nvarchar(200) 
as
begin
        if @ID is null
                return '';

      declare @name nvarchar(200);
    with LETTERS (NAME) AS
      (select NAME from dbo.LETTERCODE where ID = @ID
      union
      select NAME from dbo.TRIBUTELETTERCODE where ID = @ID)

    select top 1 @name = NAME from LETTERS;

    return coalesce(@name, '');
end