Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!drn.maxwell.syr.edu!news.maxwell.syr.edu!border1.nntp.dca.giganews.com!border2.nntp.dca.giganews.com!nntp.giganews.com!wns13feed!worldnet.att.net!attbi_s51.POSTED!53ab2750!not-for-mail From: "Marshall Spight" Newsgroups: comp.databases.theory References: Subject: Re: 4 the FAQ: Are Commercial DBMS Truly Relational? Lines: 28 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 Message-ID: NNTP-Posting-Host: 24.5.186.86 X-Complaints-To: abuse@comcast.net X-Trace: attbi_s51 1097380536 24.5.186.86 (Sun, 10 Oct 2004 03:55:36 GMT) NNTP-Posting-Date: Sun, 10 Oct 2004 03:55:36 GMT Organization: Comcast Online Date: Sun, 10 Oct 2004 03:55:36 GMT Xref: dp-news.maxwell.syr.edu comp.databases.theory:26718 "Laconic2" wrote in message news:ur6dnYyKodQZNvXcRVn-ow@comcast.com... > > "Marshall Spight" wrote in message > news:eP%9d.219935$D%.37995@attbi_s51... > > However, note that the result of an outer join is not necessarily a > > > relation, even if both of the operands are relations. > > > > You lost me. Do you mean something besides the part where > > there are no rows on the right corresponding to rows on the > > left, or do you mean something else? > > No. I meant that an outer join can introduce NULLS, and NULLS don't belong > in relations. Right, but although you certainly need an operation like this, SQL's outer join is not the only way to get it. I rather think that GROUP/UNGROUP, and result columns of relation type, are a better approach, in part because NULLs are not required. > I hope I'm not being too dogmatic about this. Not at all. Marshall