From: Michael Holt <michael@aers.ca>
To: Anibal David Acosta <aa@devshock.com>
To: pgsql-admin@postgresql.org
Subject: Re: using limit
Date: Thu, 16 Dec 2010 11:46:25 -0800
Message-ID: <4fb832d4d430b6edb5965e662c75334a@mail.gmail.com> (raw)
In-Reply-To: <002d01cb9d58$27fdabd0$77f90370$@devshock.com>
References: <001f01cb9d56$13d69790$3b83c6b0$@devshock.com>
<f3f619af829b15d8b901614cef0074ac@mail.gmail.com>
<002d01cb9d58$27fdabd0$77f90370$@devshock.com>
Yes, a limit should speed up your query from the sounds of things.
*From:* Anibal David Acosta [mailto:aa@devshock.com]
*Sent:* Thursday, December 16, 2010 11:34 AM
*To:* 'Michael Holt'; pgsql-admin@postgresql.org
*Subject:* RE: [ADMIN] using limit
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: michael@aers.ca, aa@devshock.com
Subject: Re: using limit
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