Ühel kenal päeval, L, 2007-02-17 kell 11:26, kirjutas Tom Lane: > Hannu Krosing <[EMAIL PROTECTED]> writes: > > How easy/hard would it be to create unique indexes on tinterval (unique > > here meaning non-overlapping) ? > > "Overlapping" is not an equality relation (it fails the transitive law), > so I'm not entirely sure what "unique" means in this context ...
Well, unique is usually defined as "not equal to any other". And "not equal" also fails transitive law. So I can't see, how failing it makes the defining the meaning of "unique" harder. What I mean by "unique interval" here is an interval over unique points, or just an interval which does not overlap any other interval. If our uniqueness implementation relies on reverse operation (equality) being transitive, then it can't be used for enforcing unique intervals. But it should be trivial to test at insertion time if the interval overlaps with any existing intervals, as it has to be inserted before the previous unique interval and after the next interval. In other words, unique interval index is a unique index of interval start times with extra condition that interval end time is not >= than the next intervals start. > but I can promise you you can't make it work with btree. Sorry to hear that. btree seemed like the best candidate for doing it. -- ---------------- Hannu Krosing Database Architect Skype Technologies OÜ Akadeemia tee 21 F, Tallinn, 12618, Estonia Skype me: callto:hkrosing Get Skype for free: http://www.skype.com ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
