UFN_MEMBERSHIP_GETLOOKUPID

                create function dbo.UFN_MEMBERSHIP_GETLOOKUPID
                (
                    @ID uniqueidentifier
                )
                returns nvarchar(100) as begin
                    if @ID is null
                        return '';

                    return isnull((select LOOKUPID from dbo.MEMBERSHIP where ID = @ID), '');
                end