Received: from malur.postgresql.org ([217.196.149.56])
 by arkaria.postgresql.org with esmtp (Exim 4.80) (envelope-from
 <pgsql-sql-owner+M37605=pgsql+2Dsql=arkaria.postgresql.org@postgresql.org>)
 id 1VyoXO-0005qM-0U
 for pgsql-sql@arkaria.postgresql.org; Thu, 02 Jan 2014 20:06:38 +0000
Received: from localhost ([127.0.0.1] helo=postgresql.org)
 by malur.postgresql.org with smtp (Exim 4.80) (envelope-from
 <pgsql-sql-owner+M37605=pgsql+2Dsql=arkaria.postgresql.org@postgresql.org>)
 id 1VyoXN-0004ww-Cn
 for pgsql-sql@arkaria.postgresql.org; Thu, 02 Jan 2014 20:06:37 +0000
Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29])
 by malur.postgresql.org with esmtp (Exim 4.80)
 (envelope-from <jonathan.katz@excoventures.com>) id 1VyoXL-0004vc-Ru
 for pgsql-sql@postgresql.org; Thu, 02 Jan 2014 20:06:35 +0000
Received: from mail-qa0-f50.google.com ([209.85.216.50])
 by magus.postgresql.org with esmtp (Exim 4.80)
 (envelope-from <jonathan.katz@excoventures.com>) id 1VyoXJ-0004Ji-CQ
 for pgsql-sql@postgresql.org; Thu, 02 Jan 2014 20:06:35 +0000
Received: by mail-qa0-f50.google.com with SMTP id i13so13690325qae.9
 for <pgsql-sql@postgresql.org>; Thu, 02 Jan 2014 12:06:31 -0800 (PST)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20130820;
 h=x-gm-message-state:subject:mime-version:content-type:from
 :in-reply-to:date:cc:content-transfer-encoding:message-id:references
 :to; bh=rDEPpBThUbfN/iSzPmlJKxYXyDnA+i3L4lHjWyw1h/k=;
 b=UcLMoYC+MhsZTkW+QGD/0D5PtTPo6wHt+GH/PgMOazMtFvU4WTZIbXL0r7wTqHjocm
 8aNOJ0a2TnnpMK4tAkiRSIM3Jqt+09uedCA+CW/AKRlJ47qym6nku6h198AgTmAl1vWb
 2XbjPnf8NdsVJ60b53UDjnywLqyFkl9WOQE+Ld1DayV67F6BSFNoq4xITJe2ojjQl820
 qEH0MA6/irBylWu3gp2F1vmn0YhfplxruBJ+5u4IRw8EhOBDlbqtBKZRe13UcJWjspMP
 BhYn6wXIh18UEFPClC2zJNRMUHd9MuB4kpwvACt/Sg2Ys8lDSvK0wqCdS/Z4yTQ91iKy
 vTMw==
X-Gm-Message-State: 
 ALoCoQlKHukTn2L/Z6HoxeB2qlKyTSavlMFltqfsmLtkgiEmLNXicQ7817oboRG87y+richmAYAs
X-Received: by 10.49.2.132 with SMTP id 4mr144099719qeu.15.1388693191647;
 Thu, 02 Jan 2014 12:06:31 -0800 (PST)
Received: from [10.0.0.28] (pool-108-6-136-93.nycmny.fios.verizon.net.
 [108.6.136.93])
 by mx.google.com with ESMTPSA id d1sm82005220qai.7.2014.01.02.12.06.30
 for <multiple recipients>
 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128);
 Thu, 02 Jan 2014 12:06:30 -0800 (PST)
Subject: Re: Index on multiple columns VS multiple index
Mime-Version: 1.0 (Apple Message framework v1283)
Content-Type: text/plain; charset=iso-8859-1
From: "Jonathan S. Katz" <jonathan.katz@excoventures.com>
In-Reply-To: 
 <CAOBG12nTYcd-QfhLBg2UQK1cRQwQh8_0bcjqhwrgac0DDTrAaw@mail.gmail.com>
Date: Thu, 2 Jan 2014 15:06:28 -0500
Cc: "pgsql-sql@postgresql.org" <pgsql-sql@postgresql.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <B8172ABC-0EB4-4859-8D93-A7CB11DA6785@excoventures.com>
References: 
 <CAOBG12m10zcGwHY_g8+Mwhs2sXjBvue5EqidHGj+pZtH3XFCXw@mail.gmail.com>
 <260BFF81-D9DB-4A71-9D17-2BD7C1F4C343@excoventures.com>
 <CAOBG12nmg+fheEgoqk=B4zHd-6tqfwAkFt1H6G=cz6e5bXr_QQ@mail.gmail.com>
 <97DDB603-D01D-4355-872A-5913DBBC5268@excoventures.com>
 <CAO+EYw+T2Aj6xP0w4oNzPiBPdXykssRRJFO_c01dCpXQVuAqFA@mail.gmail.com>
 <CAOBG12nTYcd-QfhLBg2UQK1cRQwQh8_0bcjqhwrgac0DDTrAaw@mail.gmail.com>
To: =?iso-8859-1?Q?Brice_Andr=E9?= <brice@famille-andre.be>
X-Mailer: Apple Mail (2.1283)
X-Pg-Spam-Score: -2.6 (--)
List-Archive: <http://archives.postgresql.org/pgsql-sql>
List-Help: <mailto:majordomo@postgresql.org?body=help>
List-ID: <pgsql-sql.postgresql.org>
List-Owner: <mailto:pgsql-sql-owner@postgresql.org>
List-Post: <mailto:pgsql-sql@postgresql.org>
List-Subscribe: <mailto:majordomo@postgresql.org?body=sub%20pgsql-sql>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-sql>
X-Mailing-List: pgsql-sql
Precedence: bulk
Sender: pgsql-sql-owner@postgresql.org

On Jan 2, 2014, at 3:00 PM, Brice Andr=E9 wrote:

> But I have still one question that remains :=20
>=20
> suppose I define an index on ('a', 'b') columns, will it be useful for a =
search on 'a' column only, or will it be ignore by postgresl ?

If you define the index on ('a', 'b') in that order and are just searching =
for 'a' in your query, the query planner will use the index.

Jonathan



--=20
Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-sql