Re: prefix search in tsearch

From: Oleg Bartunov <oleg(at)sai(dot)msu(dot)su>
To: Erik Rijkers <er(at)xs4all(dot)nl>
Cc: pgsql-docs(at)postgresql(dot)org
Subject: Re: prefix search in tsearch
Date: 2010-09-01 08:44:28
Message-ID: Pine.LNX.4.64.1009011240100.9267@sn.sai.msu.ru
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Erik,

I think it'd be more clear if you say not 'stemmed', but processed in
according to configuration. Here is an example:

$SHAREDIR/tsearch_data/my_synonyms.syn contains one line:
one 1

CREATE TEXT SEARCH DICTIONARY my_synonym (
TEMPLATE = synonym,
SYNONYMS = my_synonyms
);

ALTER TEXT SEARCH CONFIGURATION english
ALTER MAPPING FOR asciiword
WITH my_synonym, english_stem;

test=# select 'one'::tsvector @@ to_tsquery('english','one:*');
?column?
----------
f
(1 row)

because 'one' was processed by my_synonym dictionary.

test=# select ts_debug('english','one');
ts_debug
------------------------------------------------------------------------------
(asciiword,"Word, all ASCII",one,"{my_synonym,english_stem}",my_synonym,{1})
(1 row)

On Tue, 31 Aug 2010, Erik Rijkers wrote:

> [docs from cvs HEAD]
>
> I found the text-search documentation a little unclear about 'prefix search'; specifically, the
> examples do not show that the so-called 'prefix' is first stemmed, before it is used as prefix.
>
> For instance, the following can be a little surprising:
>
> SELECT to_tsvector( 'postgraduate' ) @@ to_tsquery( 'postgres:*' );
> ?column?
> ----------
> t
> (1 row)
>
> Because prefix search is such an important functionality I think this should be better explained,
> which I hope the attached doc-patch does.
>
> (In textsearch.sgml is another mention + example of prefix search, perhaps it should be extended a
> little there too - which I'm happy to do as well, but I first wanted to see if you agree that it
> is a little too obscure as it stands)
>
>
> Erik Rijkers
>

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

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