Re: Question about trigram GIST index

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От Robert DiFalco
Тема Re: Question about trigram GIST index
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Msg-id CAAXGW-yWdFTFSLquOH2qNY4BpL95VGKPAObK3ECdnT2i-zMfzw@mail.gmail.com
обсуждение исходный текст
Ответ на Re: Question about trigram GIST index  (Giuseppe Broccolo <giuseppe.broccolo@2ndquadrant.it>)
Список pgsql-performance
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I'm pretty sure '%John%' uses the index.

explain analyze verbose SELECT name FROM wai_users WHERE lower(name) LIKE '%john%';

                                                          QUERY PLAN                                                          
------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on public.wai_users  (cost=53.45..1345.46 rows=900 width=14) (actual time=18.474..32.093 rows=1596 loops=1)
   Output: name
   Recheck Cond: (lower((wai_users.name)::text) ~~ '%john%'::text)
   ->  Bitmap Index Scan on idx_user_name  (cost=0.00..53.41 rows=900 width=0) (actual time=18.227..18.227 rows=1596 loops=1)
         Index Cond: (lower((wai_users.name)::text) ~~ '%john%'::text)
 Total runtime: 33.662 ms
(6 rows)


On Thu, Dec 18, 2014 at 10:00 AM, Giuseppe Broccolo <giuseppe.broccolo@2ndquadrant.it> wrote:
I'm not sure about the '%' operator, but I'm sure that the GIST index will never be used in the

  SELECT * FROM users WHERE lower(name) LIKE '%john%';

query; it is used for left or right anchored search, such as 'john%' or '%john'.

Giuseppe.
--
Giuseppe Broccolo - 2ndQuadrant Italy
PostgreSQL Training, Services and Support
giuseppe.broccolo@2ndQuadrant.it | www.2ndQuadrant.it

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