Re: [GENERAL] 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.vondra@2ndquadrant.com <mailto:tomas.vondra@2ndquadrant.com>>wrote:

    On 12/30/2016 12:33 AM, David G. Johnston wrote:

        On Thu, Dec 29, 2016 at 4:21 PM, Job <Job@colliniconsulting.it
        <mailto:Job@colliniconsulting.it>
        <mailto:Job@colliniconsulting.it
        <mailto:Job@colliniconsulting.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