X-Original-To: pgsql-sql-postgresql.org@localhost.postgresql.org
Received: from localhost (unknown [200.46.204.2])
	by svr1.postgresql.org (Postfix) with ESMTP id 4666FD1D5A3
	for <pgsql-sql-postgresql.org@localhost.postgresql.org>;
	Wed, 19 Nov 2003 07:20:30 +0000 (GMT)
Received: from svr1.postgresql.org ([200.46.204.71])
	by localhost (neptune.hub.org [200.46.204.2]) (amavisd-new, port 10024)
	with ESMTP id 14556-04
	for <pgsql-sql-postgresql.org@localhost.postgresql.org>;
	Wed, 19 Nov 2003 03:20:00 -0400 (AST)
Received: from news.hub.org (news.hub.org [200.46.204.72])
	by svr1.postgresql.org (Postfix) with ESMTP id 6AB44D1C4EE
	for <pgsql-sql@postgresql.org>; Wed, 19 Nov 2003 03:19:59 -0400 (AST)
Received: from news.hub.org (news.hub.org [200.46.204.72])
	by news.hub.org (8.12.9/8.12.9) with ESMTP id hAJ7JwO4099188
	for <pgsql-sql@postgresql.org>; Wed, 19 Nov 2003 07:19:59 GMT
	(envelope-from news@news.hub.org)
Received: (from news@localhost)
	by news.hub.org (8.12.9/8.12.9/Submit) id hAJ6shbK093495
	for pgsql-sql@postgresql.org; Wed, 19 Nov 2003 06:54:43 GMT
From: "Randolf Richardson, DevNet SysOp 29" <rr@8x.ca>
X-Newsgroups: comp.databases.postgresql.sql
Subject: Re: Expressional Indexes
Date: Wed, 19 Nov 2003 06:54:43 +0000 (UTC)
Organization: Inter-Corporate Computer & Network Services, Inc.
Lines: 50
Message-ID: <Xns9437E70E5112rr8xca@200.46.204.72>
References: <7141E2A2-04BE-11D8-81AE-0005029FC1A7@myrealbox.com>
	<200310221239.58302.josh@agliodbs.com>
	<18349.1066851898@sss.pgh.pa.us>
	<200310221322.26013.josh@agliodbs.com>
	<Xns9435D8D7BF744rr8xca@200.46.204.72>
	<877k1w6fcv.fsf@stark.dyndns.tv>
X-Complaints-To: usenet@news.hub.org
User-Agent: Xnews/5.04.25
X-Face: 
 +kXh]<cm0}l<Fvzd*?E]I7=Ug!X`>8'{:R`HzXla-aT~$s8a+C)k/B%RBr$_3sP`[kA}cl7#mD^9Z:oM`HpoC_kUEH['RZ*Ob%pz\ww^q&x)~zc`.xd]VQ4WN/3t2nS-<I>BvI%LF\B4:\9$EI:/|<)`?8I_;
	xzG@SOYFir/gk_eB4"Rl43-h%)8O0sR$b&Mp3XHR(0j=
X-Face-Author: Randolf Richardson (composed with Adobe Photoshop)
To: pgsql-sql@postgresql.org
X-Virus-Scanned: by amavisd-new at postgresql.org
X-Archive-Number: 200311/236
X-Sequence-Number: 16051

>> For example, if I want to index on a date field but only have the index 
>> keep track of the most recent 30 days (and then create a secondary
>> index for all dates) so as to improve performance on more heavily
>> loaded systems. 
>> 
>> Am I understanding this new terminology correctly?  Thanks in advance. 
> 
> No, you could do the above using "partial indexes" but it wouldn't work
> very well in this case because the "last 30 days" keeps moving and you
> would have to keep redefining the index periodically.

    	For the application I will need to develop in the future, it would be 
okay for this index to hold data more than 30 days old, and then be 
redefined on a monthly basis along with regular database vacuuming (and 
other maintenance).

    	Could this be done with a "partial index" as follows?

    	    	CREATE INDEX my_index on my_table (create_date)
    	    	  WHERE (create_date > age(timestamp '30 days'));

    	If I've made any mistakes here, please don't hesitate to let me know 
because the age() function is new to me.

> It also wouldn't really help performance.

    	Really?  A smaller index would result in fewer comparisons behind-the-
scenes though, wouldn't it?

> Expression Indexes are just more powerful "functional indexes". In 7.3
> they could be used for indexing expressions like "lower(foo)". In 7.4
> they're more powerful and you can index expressions other than simple
> function calls. 
[sNip]

    	So an "Expression Index" could, for example, be used to sort alpha-
numeric data in a case-insensitive manner?  I just want to make sure I'm 
understanding this correctly.

    	Thanks.

-- 
Randolf Richardson - rr@8x.ca
Inter-Corporate Computer & Network Services, Inc.
Vancouver, British Columbia, Canada
http://www.8x.ca/

This message originated from within a secure, reliable,
high-performance network ... a Novell NetWare network.