From pgsql-general-owner+M10387@postgresql.org Mon Jun 4 22:02:55 2001 Return-path: Received: from postgresql.org (webmail.postgresql.org [216.126.85.28]) by candle.pha.pa.us (8.10.1/8.10.1) with ESMTP id f5522tc28169 for ; Mon, 4 Jun 2001 22:02:55 -0400 (EDT) Received: from postgresql.org.org (webmail.postgresql.org [216.126.85.28]) by postgresql.org (8.11.3/8.11.1) with SMTP id f5520BE14492; Mon, 4 Jun 2001 22:00:11 -0400 (EDT) (envelope-from pgsql-general-owner+M10387@postgresql.org) Received: from sss.pgh.pa.us ([192.204.191.242]) by postgresql.org (8.11.3/8.11.1) with ESMTP id f551hHE09364 for ; Mon, 4 Jun 2001 21:43:17 -0400 (EDT) (envelope-from tgl@sss.pgh.pa.us) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.11.3/8.11.3) with ESMTP id f551gwR09928; Mon, 4 Jun 2001 21:42:58 -0400 (EDT) To: Rasmus Resen Amossen cc: pgsql-general@postgresql.org Subject: Re: [GENERAL] Re: Updating views In-Reply-To: <3B1C16EC.8D9FB57B@rhk.dk> References: <20010605001048.A2133@lorien.net> <3B1C16EC.8D9FB57B@rhk.dk> Comments: In-reply-to Rasmus Resen Amossen message dated "Tue, 05 Jun 2001 01:17:00 +0200" Date: Mon, 04 Jun 2001 21:42:57 -0400 Message-ID: <9925.991705377@sss.pgh.pa.us> From: Tom Lane Precedence: bulk Sender: pgsql-general-owner@postgresql.org Status: OR Rasmus Resen Amossen writes: > OK, but I can't see how to make a single rule that allows me to update > an arbitray set of attributes from an arbitray where-clause. The reason the system doesn't do that for you is that it's *hard* to figure out what to do for an arbitrary where-clause. An automatic rule has no chance of doing the right thing, because the right thing depends on what you intend. For example, if your view has select ... where a>5; what do you think ought to happen if someone tries to insert a row with a<5? Is that an error? A no-op? Does the row go in anyway, you just can't see it in the view? Does the row go into some other table instead? Is it OK to change the A column at all? It all depends on the semantics of your database design. So you have to figure out what you want and write rules that do it. The mechanics of the rule are not that painful once you've decided what the reverse mapping from inserted/updated data to underlying tables ought to be. One thing that may help is to realize that you don't need a separate rule for each combination of set of attributes that might be updated. "new.*" is defined for all columns including the ones that didn't change, so you can just do something like update ... set f1 = new.f1, f2 = new.f2, ... without worrying about just which columns the user tried to update. Likewise, the where clause in the user's query is not yours to worry about; that condition gets added onto the stuff in your rule. > In other words: I want to make the update of 'exview' transparent to > 'extable'. If it's really transparent, one wonders why you bothered with a view at all. Useful views tend to be nontrivial mappings of the underlying data, which is why it's nontrivial to figure out what the reverse mapping ought to be. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://www.postgresql.org/search.mpl