Re: Searching a gin index

James,

syntax is documented on
http://www.postgresql.org/docs/8.3/static/textsearch-tables.html#TEXTSEARCH-TABLES-SEARCH
and in the Introduction
http://www.postgresql.org/docs/8.3/static/textsearch-intro.html#TEXTSEARCH-MATCHING
text-search operator was specified for tsvector @@ tsquery.
You did wrong twice, you didn't specified type tsvector and you
forgot about coalesce.

There is general rule for partial indexes - you should use the same
expression in query as you used in create index command.

Oleg
On Fri, 6 Feb 2009, James Dooley wrote:

> Oleg, but I am only interested in whether or not the syntax of my
> search-query is correct.
>
> Having created the index as I mentioned above, would the correct way of
> searching and using that index be
>
> ... AND (title || '' || description || '' || name) @@ plainto_tsquery('car')
>
> or should it be as Richard just mentioned
>
> ... AND to_tsvector(title || '' || description || '' || name) @@
> plainto_tsquery('car')
>
> or some other way ?
>
>
>
> On Fri, Feb 6, 2009 at 3:30 PM, Richard Huxton <dev(at)archonet(dot)com> wrote:
>
>> James Dooley wrote:
>>> Hi again,
>>>
>>> I have set my configuration as default and I have created a GIN index on
>>> three columns, like this
>>>
>>> create index textsearch_index on products using gin(strip( to_tsvector(
>>> 'my_config', title || '' || description || '' || name)))
>>>
>>> Searching these columns the way I have
>>>
>>> ... AND (title || '' || description || '' || name) @@
>> plainto_tsquery('car')
>>>
>>> seems not to be correct since it's taking as much time as non-indexed.
>>
>> PG's planner isn't smart enough to transform a complex expression so as
>> to use a functional index (which is what you've got). You need to
>> mention the function explicitly.
>>
>> So, if you had:
>> CREATE INDEX lowercase_idx ON mytable ( lower(mycolumn) )
>> You then need to search against "lower(mycolumn)" and not just expect
>> the planner to notice that mycolumn="abc" could use the index.
>>
>> The following should work for you as a starting point:
>>
>> CREATE TABLE tsearch_tbl (id SERIAL, title text, body text,
>> PRIMARY KEY (id));
>>
>> INSERT INTO tsearch_tbl (title, body)
>> SELECT 'title number ' || n, 'This is body number ' || n
>> FROM generate_series(1,9999) n;
>>
>> ANALYSE tsearch_tbl;
>>
>> CREATE INDEX tsearch_tbl_words_idx ON tsearch_tbl USING gin (
>> to_tsvector('english', title || body) );
>>
>> EXPLAIN ANALYSE SELECT * FROM tsearch_tbl WHERE to_tsvector('english',
>> title || body) @@ to_tsquery('17');
>> QUERY PLAN
>>
>>
>> -------------------------------------------------------------------------------------------------------------------------------
>> Bitmap Heap Scan on tsearch_tbl (cost=4.34..34.76 rows=10 width=45)
>> (actual time=0.067..0.067 rows=1 loops=1)
>> Recheck Cond: (to_tsvector('english'::regconfig, (title || body)) @@
>> to_tsquery('17'::text))
>> -> Bitmap Index Scan on tsearch_tbl_words_idx (cost=0.00..4.34
>> rows=10 width=0) (actual time=0.059..0.059 rows=1 loops=1)
>> Index Cond: (to_tsvector('english'::regconfig, (title || body))
>> @@ to_tsquery('17'::text))
>> Total runtime: 0.121 ms
>>
>>
>> Note that you'll have problems if any of your text-fields contain nulls
>> (since null || anything = null).
>>
>> Personally, unless I'm dealing with a large table, I like to have a
>> separate tsvector column which I keep up to date with triggers. It makes
>> it easier to debug problems.
>>
>> --
>> Richard Huxton
>> Archonet Ltd
>>
>

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