Path: newssvr20.news.prodigy.com!newsmst01.news.prodigy.com!prodigy.com!logbridge.uoregon.edu!newsfeed.berkeley.edu!ucberkeley!cyclone-sf.pbi.net!216.218.192.242!news.he.net!chekhov.conxion.net!news.oracle.com!not-for-mail From: "Mikito Harakiri" Newsgroups: comp.databases.theory References: Subject: Re: View Updates Problem Statement Lines: 51 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 Message-ID: Date: Mon, 8 Sep 2003 18:02:15 -0700 NNTP-Posting-Host: 130.35.179.109 X-Trace: news.oracle.com 1063069873 130.35.179.109 (Mon, 08 Sep 2003 18:11:13 PDT) NNTP-Posting-Date: Mon, 08 Sep 2003 18:11:13 PDT Xref: newssvr20.news.prodigy.com comp.databases.theory:21351 "Mikito Harakiri" wrote in message news:Yw97b.27$741.210@news.oracle.com... > 3. Constraints are views that evaluate to constants. For example, if we > define > > view V3 > select max(sal) from ( > select sal from emp > union > select 1000 from DEE > ) > > then constraint "each emp has salary no more than 1000" can algebraically be > written as > > V3*x = 1000 > > where "V3*x" means view V3 applied to a set of base relations x, and "1000" > means an output relation that has one tuple with a single value 1000. Small increment, sorry. It is even better to write constraint equation as view V3 select max(sal)/1000 from ( select sal from emp union select 1000 from DEE ) V3*x = DEE or still even better view V3 select 1000 from DEE minus select max(sal) from ( select sal from emp union select 1000 from DEE ) V3*x = DUM (Equations that evaluate to 0 are math favorits:-)