From: Anibal David Acosta <aa@devshock.com>
To: 'Michael Holt' <michael@aers.ca>
To: pgsql-admin@postgresql.org
Subject: Re: using limit
Date: Thu, 16 Dec 2010 16:33:42 -0300
Message-ID: <002d01cb9d58$27fdabd0$77f90370$@devshock.com> (raw)
In-Reply-To: <f3f619af829b15d8b901614cef0074ac@mail.gmail.com>
References: <001f01cb9d56$13d69790$3b83c6b0$@devshock.com>
<f3f619af829b15d8b901614cef0074ac@mail.gmail.com>
Is a table with 10 million of rows with a primary key but conditions used in
select are not part of PK.
My table is like this:
Column 1 - PK
Column 2 - Indexed
Column 3 - Indexed
Column 2 and Column 3 are Indexed in the same index but they are not mark as
unique or PK
The Query is like this:
Select column1 from myTable where Column2 between X and Y
I am expecting just one record
De: Michael Holt [mailto:michael@aers.ca]
Enviado el: jueves, 16 de diciembre de 2010 04:23 p.m.
Para: Anibal David Acosta; pgsql-admin@postgresql.org
Asunto: RE: [ADMIN] using limit
This really depends on the type of query you're talking about. If there's
only one row in the table you're querying then no, I don't think it'll
change anything. If you're querying a single row using a primary key it
shouldn't change anything. If you're doing an aggregate query, say a sum of
a bunch of rows, it also won't improve performance.
If you're doing a query on a table with multiple rows and not filtering by a
primary key or other unique index then yes, it will improve the query.
From: pgsql-admin-owner@postgresql.org
[mailto:pgsql-admin-owner@postgresql.org] On Behalf Of Anibal David Acosta
Sent: Thursday, December 16, 2010 11:19 AM
To: pgsql-admin@postgresql.org
Subject: [ADMIN] using limit
Hi
I really like to do efficient SQL queries so, my question is if I am
expecting no more than one row from a select, using the LIMIT 1 could
improve the performance?
If I use my logic, the LIMIT 1 instruction tell to postgres that stop
searching when found 1 record, but maybe it is unnecessary
Thanks
Anibal
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To: pgsql-admin@postgresql.org
Cc: aa@devshock.com, michael@aers.ca
Subject: Re: using limit
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