if (OBJECT_ID('Ponentes') is null)
begin
	if (OBJECT_ID('OtrosPonentes') is not null)
		EXEC sp_rename 'dbo.OtrosPonentes', 'Ponentes'
	else
		create table Ponentes (
			evento_key uniqueidentifier not null,
			elt uniqueidentifier not null,
			constraint PK_Ponentes primary key(evento_key, elt),
			constraint FK_Ponentes_Evento foreign key (evento_key) references Evento,
			constraint FK_Ponentes_Persona foreign key (elt) references Persona)
end
go

insert into Ponentes (evento_key, elt)
	select e.Id, e.Ponente 
		from Evento e 
		where e.Ponente is not null and e.Ponente not in (select p.elt from Ponentes p where p.evento_key = e.Id)
go