UFN_EVENTDESIGNATION_ONEDEFAULT

            CREATE function dbo.UFN_EVENTDESIGNATION_ONEDEFAULT(
                @EVENTID uniqueidentifier,
                @DEFAULT bit
                )

                returns bit
                with execute as caller
                as begin
                  declare @DUPLICATECOUNT int;

                  select
                    @DUPLICATECOUNT = count(ID)
                  from
                    dbo.EVENTDESIGNATION
                  where
                    EVENTID = @EVENTID 
                    and [DEFAULT] = 1

                  if @DUPLICATECOUNT <= 1
                    return 1;

                  return 0;
            end