Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!drn.maxwell.syr.edu!news.maxwell.syr.edu!fu-berlin.de!uni-berlin.de!not-for-mail From: Kenneth Downs Newsgroups: comp.databases.theory Subject: Re: Unique Keys Date: Fri, 26 Nov 2004 07:00:40 -0500 Lines: 33 Message-ID: <8gij72-46a.ln1@pluto.downsfam.net> References: <1101387601.990897.214300@f14g2000cwb.googlegroups.com> <1101395692.845672.222270@z14g2000cwz.googlegroups.com> <04eh72-nan.ln1@pluto.downsfam.net> <1101405872.089624.49260@z14g2000cwz.googlegroups.com> <1101463721.289490.232110@f14g2000cwb.googlegroups.com> Reply-To: sameas@email.address Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7Bit X-Trace: news.uni-berlin.de HDGZStJzYHaRntdNDzCI/AauJMsg9bmY7qTawDWDOjW3DYxYL/ X-Orig-Path: pluto.downsfam.net!news User-Agent: KNode/0.7.7 Xref: dp-news.maxwell.syr.edu comp.databases.theory:28641 Tony Andrews wrote: > Kenneth Downs wrote: >> I would suggest it is more useful to define the equality operator as > such: >> >> where x = (a,b) >> and y = (c,d) >> >> x = y iff (a <= c <= b) OR (a <= d <= b) >> >> It is the equality operator definition that makes it a declarative > unique >> constraint exactly the same as any other, and also makes possible > simple >> foreign keys. Now we have: >> >> CREATE TABLE reservations ( >> hotel_room char(4), >> span DATEINTERVAL ) >> PRIMARY KEY (hotel_room,span) > > Yes, but only by subverting the traditional meaning of "equals"! So > what do you do now if you want to know if the 2 DATEINTERVALs really > are the same? > Perhaps you would be more comfortable with the OO term? Operator Overloading? -- Kenneth Downs