Re: Special index for "like"-based query

On 12/30/2016 12:46 AM, David G. Johnston wrote:
> On Thu, Dec 29, 2016 at 4:38 PM, Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)com <mailto:tomas(dot)vondra(at)2ndquadrant(dot)com>>wrote:
>
> On 12/30/2016 12:33 AM, David G. Johnston wrote:
>
> On Thu, Dec 29, 2016 at 4:21 PM, Job <Job(at)colliniconsulting(dot)it
> <mailto:Job(at)colliniconsulting(dot)it>
> <mailto:Job(at)colliniconsulting(dot)it
> <mailto:Job(at)colliniconsulting(dot)it>>>wrote:
>
> Hello,
>
> in Postgresql 9.6 we have a query running on a very large table
> based, in some cases, on a like statement:
>
> ... WHERE FIELD='CODE' OR FIELD LIKE 'CODE_%'
>
> Which type of index can i create to speed to the search when the
> "like" case happens?
>
>
> ​GIST​
>
> https://www.postgresql.org/docs/9.6/static/pgtrgm.html
> <https://www.postgresql.org/docs/9.6/static/pgtrgm.html>
>
> ​https://www.postgresql.org/docs/9.6/static/btree-gist.html
> <https://www.postgresql.org/docs/9.6/static/btree-gist.html>
> ​
>
>
> For prefix queries, it's also possible to use simple btree index
> with varchar_pattern_ops.
>
> https://www.postgresql.org/docs/9.6/static/indexes-opclass.html
> <https://www.postgresql.org/docs/9.6/static/indexes-opclass.html>
>
>
> Even knowing that this feature exists I don't know that I could have
> found it within a reasonable amount of time in its present location. A
> few cross-references from elsewhere (probably at least the functions
> part of the documentation) would make learning about the capability a
> lot easier.
>

Well, it's referenced right from the "Indexes" part of the documentation
(right at the beginning of "Index Types"):

https://www.postgresql.org/docs/9.6/static/indexes.html

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services