"Martijn van Oosterhout" <kleptog@xxxxxxxxx> writes: > On Fri, Jun 22, 2007 at 07:38:01PM +0300, Tzahi Fadida wrote: >> Let me simplify it in lamer terms. >> Basically, you have a cycle in your relations schema. i.e. >> rel A: att-x, att-y >> rel B: att-y, att-z >> rel C: att-z, att-x >> >> The only way to join these three without loosing a lot of information (aside >> from some very weird corner cases which i won't mention here), is to use my >> full disjunctions which is probably most certainly the only implementation of >> the operation in existence to calculate the general case (which you can see >> above). > > FWIW, with this simple description I finally worked out what full > disjunctions are and why you can't do them (efficiently) in SQL. I'm still lost. I can see how it would be hard to join these together but I'm not sure what result I would be after. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com
