To: Michael Glaesmann <grzm@myrealbox.com>
Cc: pgsql-novice@postgresql.org
Subject: Re: Functional index problems. (Was: Many joins: monthly summaries
	S-L--O--W)
In-reply-to: <461424BA-04B2-11D8-81AE-0005029FC1A7@myrealbox.com> 
References: <461424BA-04B2-11D8-81AE-0005029FC1A7@myrealbox.com>
Comments: In-reply-to Michael Glaesmann <grzm@myrealbox.com>
	message dated "Thu, 23 Oct 2003 02:07:53 +0900"
Date: Wed, 22 Oct 2003 13:44:50 -0400
Message-ID: <17556.1066844690@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Michael Glaesmann <grzm@myrealbox.com> writes:
> Searching for ways to improve performance, I tried to create a index on 
> the extract function, but for some reason I couldn't get it to work. 
> Following the documentation for CREATE INDEX and EXTRACT, I tried

> CREATE INDEX dborders_extract_month_idx ON dborders (EXTRACT(MONTH from 
> date));
> ERROR:  parser: parse error at or near "(" at character 61

You can't do that in pre-7.4 releases; the syntax of a functional index
can only be "ON table (func(col1,col2,...))" --- that is, a simple,
standard-notation function applied to one or more columns of the table.
So to do this, you'd need to create an intermediate function along
the lines of "month_trunc(date)"; and you'd have to use it in your
queries as well as in the index definition.

7.4 is more flexible though --- it will take the above as long as you
put an extra set of parentheses in there...

			regards, tom lane