From: Vitalii Tymchyshyn <tivv00@gmail.com>
To: Adarsh Sharma <adarsh.sharma@orkash.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Re-Reason of Slowness of Query
Date: Wed, 23 Mar 2011 12:37:58 +0200
Message-ID: <4D89CD86.4000008@gmail.com> (raw)
In-Reply-To: <4D89C926.8050009@orkash.com>
References: <4D89BABF.4080806@orkash.com>
<4D89BCD6.6040604@gmail.com>
<4D89C704.5080603@orkash.com>
<4D89C778.6050805@gmail.com>
<4D89C926.8050009@orkash.com>
23.03.11 12:19, Adarsh Sharma ???????(??):
> Vitalii Tymchyshyn wrote:
>> 23.03.11 12:10, Adarsh Sharma ???????(??):
>>> I just want to retrieve that id 's from page_content which do not
>>> have any entry in clause2 table.
>>>
>> Then
>> select distinct(p.crawled_page_id) from page_content p
>> where NOT EXISTS (select 1 from clause2 c where c.source_id =
>> p.crawled_page_id);
>> is correct query.
>>
>
> I can't understand how*select 1 from clause2 c where c.source_id =
> p.crawled_page_id works too, *i get my output .
>
> What is the significance of 1 here.
No significance. You can put anything there. E.g. "*". Simply arbitrary
constant. Exists checks if there were any rows, it does not matter which
columns are there or what is in this columns.
Best regards, Vitalii Tymchyshyn
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: tivv00@gmail.com, adarsh.sharma@orkash.com
Subject: Re: Re-Reason of Slowness of Query
In-Reply-To: <4D89CD86.4000008@gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox