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.brocc...@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.brocc...@2ndquadrant.it | www.2ndQuadrant.it
>

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