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Message-ID: <4D89CD86.4000008@gmail.com>
Date: Wed, 23 Mar 2011 12:37:58 +0200
From: Vitalii Tymchyshyn <tivv00@gmail.com>
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To: Adarsh Sharma <adarsh.sharma@orkash.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Re-Reason of Slowness of Query
References: <4D89BABF.4080806@orkash.com> <4D89BCD6.6040604@gmail.com>
	<4D89C704.5080603@orkash.com> <4D89C778.6050805@gmail.com>
	<4D89C926.8050009@orkash.com>
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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


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    23.03.11 12:19, Adarsh Sharma &#1085;&#1072;&#1087;&#1080;&#1089;&#1072;&#1074;(&#1083;&#1072;):
    <blockquote cite="mid:4D89C926.8050009@orkash.com" type="cite">
      <meta content="text/html; charset=ISO-8859-1"
        http-equiv="Content-Type">
      Vitalii Tymchyshyn wrote:
      <blockquote cite="mid:4D89C778.6050805@gmail.com" type="cite">
        <meta content="text/html; charset=ISO-8859-1"
          http-equiv="Content-Type">
        23.03.11 12:10, Adarsh Sharma &#1085;&#1072;&#1087;&#1080;&#1089;&#1072;&#1074;(&#1083;&#1072;):
        <blockquote cite="mid:4D89C704.5080603@orkash.com" type="cite">
          <meta content="text/html; charset=ISO-8859-1"
            http-equiv="Content-Type">
          I just want to retrieve that id 's from page_content which do
          not have
          any entry in clause2 table.<br>
          <br>
        </blockquote>
        Then <br>
        select distinct(p.crawled_page_id) from page_content p<br>
        &nbsp;where NOT EXISTS (select 1 from&nbsp; clause2 c where c.source_id =
        p.crawled_page_id);<br>
        is correct query.<br>
        <br>
      </blockquote>
      <br>
      I can't understand how<b> select 1 from&nbsp; clause2 c where
        c.source_id =
        p.crawled_page_id works too, </b>i get my output .<br>
      <br>
      What is the significance of 1 here.<br>
    </blockquote>
    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.<br>
    <br>
    Best regards, Vitalii Tymchyshyn<br>
    <br>
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