From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: pgsql-performance@postgresql.org
Subject: Re: extract(year from date) doesn't use index but maybe could?
Date: Sun, 19 Apr 2015 19:42:12 +0200
Message-ID: <5533E8F4.2050400@2ndquadrant.com> (raw)
In-Reply-To: <CADhq2b51G0QrjNz_vH6e_SLyu=tR0A0G0zHhFsP7rqRr+6FA3w@mail.gmail.com>
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On 04/19/15 19:16, Jon Dufresne wrote:
> Given the table:
>
> CREATE TABLE dates (id SERIAL, d DATE NOT NULL, t TEXT NOT NULL)
>
> With an *index* on field d. The following two queries are functionally
> equivalent:
>
> 1. SELECT * FROM dates WHERE d >= '1900-01-01'
> 2. SELECT * FROM dates WHERE EXTRACT(year from d) >= 1900'
>
> By functionally equivalent, they will return the same result set.
>
> Query 2 does not use the index, adding a performance cost. It seems
> there is an opportunity for optimization to handle these two queries
> equivalently to take advantage of the index.
Or you might try creating an expression index ...
CREATE INDEX date_year_idx ON dates((extract(year from d)));
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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Subject: Re: extract(year from date) doesn't use index but maybe could?
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