> does this work correctly? > > UPDATE Reservations > SET ReservedBy = r2.ReservedBy > FROM Reservations r > inner > join Reservations r2 > on r.ParentReservationID = r2.ReservationID > WHERE r.ReservedBy IS NULL Oh dear god. Even your suggestion, rudy, my favourite SQL guru, did not work; I got the same error message "The table 'Reservations' is ambiguous". I suppose I could create a copy of the table and make it work that way. I just hate to give in like that. But if all else fails, that's what I'll do.