From: | Oleg Bartunov <oleg(at)sai(dot)msu(dot)su> |
---|---|
To: | Mike Christensen <imaudi(at)comcast(dot)net> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Question about fulltext search and to_tsvector function |
Date: | 2008-10-17 14:48:55 |
Message-ID: | Pine.LNX.4.64.0810171831390.15810@sn.sai.msu.ru |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-general |
Mike,
1. always separate attributes by blank unless you sure words can span different
columns, e.g., title||' '||description
2. use coalesce to avoid unexpected NULL string
Oleg
On Thu, 16 Oct 2008, Mike Christensen wrote:
> Okay this one's driving me crazy.
>
> Should there be any difference between the following queries:
>
> SELECT R.Title FROM Recipes R
> WHERE (to_tsvector('english', title || description) @@
> plainto_tsquery('Cake'));
>
> and
>
> SELECT R.Title FROM Recipes R
> WHERE (to_tsvector('english', description || title) @@
> plainto_tsquery('Cake'));
>
>
> This query should search for the word 'Cake' in either the description OR the
> title field, correct? The order should not matter. However, in the first
> query I get 6 results and in the second I get 9.
>
> Furthermore, if I do:
>
> SELECT R.Title FROM Recipes R
> WHERE (to_tsvector('english', title) @@ plainto_tsquery('Cake'));
>
> I get 10 results and if I do:
>
> SELECT R.Title FROM Recipes R
> WHERE (to_tsvector('english', title || coalesce(description, '')) @@
> plainto_tsquery('Cake'));
>
> I get 7 results. Shouldn't the first query result in a subset of the second
> query? The first query returns several rows the second one doesn't return,
> and vice-versa! This function is completely confusing me!!
>
> I would greatly appreciate anyone who could explain exactly how this works.
> It's most likely something stupid I'm doing that is the result of me not
> getting enough sleep..
>
> Mike
>
>
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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