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From: Joshua D. Drake <jd@commandprompt.com>
To: Robins Tharakan <tharakan@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: count * performance issue
Date: Mon, 10 Mar 2008 20:08:44 -0700
Message-ID: <20080310200844.2281f0e8@jd-laptop> (raw)
In-Reply-To: <36af4bed0803101957u6078127fq78dc3384fe78de5d@mail.gmail.com>
References: <f966c2ee0803052142l6a105678jfe2da92a0d9371@mail.gmail.com>
	<47D00DB2.7040007@emolecules.com>
	<18451.1204824562@sss.pgh.pa.us>
	<200803071727.36146.josh@agliodbs.com>
	<13345.1204940295@sss.pgh.pa.us>
	<87r6eia9tz.fsf@oxford.xeocode.com>
	<12ba3bf00803101354w15b023e1o237f564a1b01105f@mail.gmail.com>
	<Pine.GSO.4.64.0803101853090.25041@westnet.com>
	<36af4bed0803101957u6078127fq78dc3384fe78de5d@mail.gmail.com>

On Tue, 11 Mar 2008 08:27:05 +0530
"Robins Tharakan" <tharakan@gmail.com> wrote:

> SELECT COUNT(*) from table WHERE indexed_field IS NULL
> +
> SELECT COUNT(*) from table WHERE indexed_field IS NOT NULL

If the selectivity is appropriate yes. However if you have 1 million
rows, and 200k of those rows are null (or not null), it is still going
to seqscan.

joshua d. drake

-- 
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