UFN_REGISTRANT_GETKEYNAME

            create function dbo.UFN_REGISTRANT_GETKEYNAME
            (
                @ID uniqueidentifier
            ) 
            returns nvarchar(154) 
            with execute as caller
            as
            begin
                declare @KEYNAME nvarchar(154)

                select 
                    @KEYNAME = case when REGISTRANT.CONSTITUENTID is not null then
                        (select KEYNAME from dbo.CONSTITUENT where ID = (REGISTRANT.CONSTITUENTID))
                    else
                        (select KEYNAME from dbo.CONSTITUENT where ID =
                            (select (GUESTOF.CONSTITUENTID) from dbo.REGISTRANT as GUESTOF where GUESTOF.ID = REGISTRANT.GUESTOFREGISTRANTID))
                    end
                from 
                    dbo.REGISTRANT 
                where 
                    ID = @ID

                return @KEYNAME
            end