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From: Markus Schaber <schabi@logix-tt.com>
To: pgsql-performance@postgresql.org
Cc: pgsql-hackers@postgresql.org
Subject: Re: qsort again (was Re: [PERFORM] Strange Create Index
Date: Fri, 17 Feb 2006 11:13:41 +0100
Message-ID: <43F5A1D5.20903@logix-tt.com> (raw)
In-Reply-To: <Pine.LNX.4.62.0602162131211.20790@qnivq.ynat.uz>
References: <43F38867.6010701@gpdnet.co.uk>
	<19510.1140036968@sss.pgh.pa.us>
	<19779.1140038874@sss.pgh.pa.us>
	<43F39E53.1020009@gpdnet.co.uk>
	<20781.1140046109@sss.pgh.pa.us>
	<7.0.1.0.2.20060215194635.03b55da0@earthlink.net>
	<21615.1140052893@sss.pgh.pa.us>
	<7.0.1.0.2.20060215223710.03a7c618@earthlink.net>
	<20060216113522.GA3461@uio.no>
	<7.0.1.0.2.20060216071053.0385a1a8@earthlink.net>
	<43F481CD.2010509@logix-tt.com>
	<43F4A7D8.4050907@modgraph-usa.com>
	<29277.1140110108@sss.pgh.pa.us>
	<1140128256.9076.254.camel@archimedes>
	<43F4FDCC.2000204@logix-tt.com>
	<871wy23okp.fsf@stark.xeocode.com>
	<1140132189.9076.261.camel@archimedes>
	<Pine.LNX.4.62.0602162131211.20790@qnivq.ynat.uz>

Hi, David,

David Lang schrieb:

>> In SQL_ASCII, just take the first 4 characters (or 8, if using a 64-bit
>> sortKey as elsewhere suggested).  The sorting key doesn't need to be a
>> one-to-one mapping.

> that would violate your second contraint ( f(a)==f(b) iff (a==b) )

no, it doesn't.

When both strings are equal, then the first characters are equal, too.

If they are not equal, the constraint condition does not match.

The first characters of the strings may be equal as f(a) may be equal to
f(b) as to the other constraint.

Markus



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