From: Arthur Zakirov <a.zakirov@postgrespro.ru>
To: Cristiano Coelho <cristianocca@hotmail.com>
Cc: pgsql-bugs@postgresql.org <pgsql-bugs@postgresql.org>
Subject: Re: pg_trgm word_similarity inconsistencies or bug
Date: Sat, 28 Oct 2017 10:22:29 +0200
Message-ID: <20171028082225.GA2157@arthur.localdomain> (raw)
In-Reply-To: <CY4PR17MB13207ED8310F847CF117EED0D85A0@CY4PR17MB1320.namprd17.prod.outlook.com>
References: <CY4PR17MB13207ED8310F847CF117EED0D85A0@CY4PR17MB1320.namprd17.prod.outlook.com>
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On Fri, Oct 27, 2017 at 06:48:08PM +0000, Cristiano Coelho wrote:
> Hello all, this is related to postgres 9.6 (9.6.4) and a good description can be found here https://stackoverflow.com/questions/46966360/postgres-word-similarity-not-comparing-words
>
> But in summary, word_similarity doesn’t seem to do exactly what the docs say, since it will match trigrams from multiple words rather tan doing a word by word comparison.
>
> Below is a table with output and expected output, thanks to kiln from stackoverflow to provide it.
>
Interesting. An klin's answer from stackoverflow.com is right.
The initial example can be reduced to the next:
=# select word_similarity('sage', 'age sag');
word_similarity
-----------------
1
It computes maximum similarity using closest trigrams not considering order of
'sage' trigrams. It determines that all
trigrams from 'sage' match trigrams from 'age sag'.
Initial order of 'age sag' trigrams:
' a', ' ag', 'age', 'ge ', ' s', ' sa', 'sag', 'ag '
^ ^
|from |to
Sorted 'sage' trigrams (all of them occured within 'age sag' trigrams
continuously):
' s', ' sa', 'age', 'ge ', 'sag'
Maybe the problem should be solved by considering 'sage' trigrams
initial order.
--
Arthur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company
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To: pgsql-hackers@postgresql.org
Cc: a.zakirov@postgrespro.ru, cristianocca@hotmail.com, pgsql-bugs@postgresql.org
Subject: Re: pg_trgm word_similarity inconsistencies or bug
In-Reply-To: <20171028082225.GA2157@arthur.localdomain>
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