Re: new function for tsquery creartion

From: Dmitry Ivanov <d(dot)ivanov(at)postgrespro(dot)ru>
To: Aleksandr Parfenov <a(dot)parfenov(at)postgrespro(dot)ru>
Cc: Aleksander Alekseev <a(dot)alekseev(at)postgrespro(dot)ru>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, David Steele <david(at)pgmasters(dot)net>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: new function for tsquery creartion
Date: 2018-04-04 14:33:47
Message-ID: a269c5f0e426174dad29c474d3669e92@postgrespro.ru
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> I'm not sure about the different result for these queries:
> SELECT websearch_to_tsquery('simple', 'cat or ');
> websearch_to_tsquery
> ----------------------
> 'cat'
> (1 row)
> SELECT websearch_to_tsquery('simple', 'cat or');
> websearch_to_tsquery
> ----------------------
> 'cat' & 'or'
> (1 row)

I guess both queries should produce just 'cat'. I've changed the
definition of parse_or_operator().

> I found an odd behavior of the query creation function in case:
> SELECT websearch_to_tsquery('english', '"pg_class pg"');
> websearch_to_tsquery
> -----------------------------
> ( 'pg' & 'class' ) <-> 'pg'
> (1 row)
>
> This query means that lexemes 'pg' and 'class' should be at the same
> distance from the last 'pg'. In other words, they should have the same
> position. But default parser will interpret pg_class as two separate
> words during text parsing/vector creation.
>
> The bug wasn't introduced in the patch and can be found in current
> master. During the discussion of the patch with Dmitry, he noticed that
> to_tsquery() function shares same odd behavior:
> select to_tsquery('english', ' pg_class <-> pg');
> to_tsquery
> -----------------------------
> ( 'pg' & 'class' ) <-> 'pg'
> (1 row)

I've been thinking about this for a while, and it seems that this should
be fixed somewhere near parsetext(). Perhaps 'pg' and 'class' should
share the same position. After all, somebody could implement a parser
which would split some words using an arbitrary set of rules, for
instance "split all words containing digits". I propose merging this
patch provided that there are no objections.

--
Dmitry Ivanov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Attachment Content-Type Size
websearch_to_tsquery_v8.patch text/x-diff 43.3 KB

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