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Date: Thu, 01 Jun 2006 16:49:54 +0200
From: =?windows-1252?Q?Miroslav_=8Aulc?= <miroslav.sulc@startnet.cz>
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To: pgsql-sql@postgresql.org
Subject: Re: SELECT DISTINCT too slow
References: <447EEAF1.7040305@startnet.cz> <20060601135310.GB18513@surnet.cl>
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Well, "key" is not primary key from another table. It is just a column
in pair "key" => "value".
The structure of the table is this:

Id (primary key)
MRTPContactId (id of contact from table MRTPContact)
Key (key from pair key => value)
Value (value from pair key => value)

So I want the get the list of keys used in the table.

Miroslav Šulc



Alvaro Herrera napsal(a):
> Miroslav ?ulc wrote:
>   
>> Hello,
>>
>> I have a table with cca 400,000 rows. The table contains column "key" of
>> varchar(20) type containing 10 distinct values. I want to get out what
>> distinct values are present in the column. I use this simple query,
>> which is very slow:
>>
>> SELECT DISTINCT Key FROM MRTPContactValue
>>     
>
> You could get the universe of values from the table where this is a
> primary key, and use an IN clause (which apparently is more efficient
> than an EXISTS in some cases, but try that too) to search for values
> that exist in the MRTPContactValue table.
>
> I assume you do have the other table, don't you?
>
>   

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Well, "key" is not primary key from another table. It is just a column
in pair "key" =&gt; "value".<br>
The structure of the table is this:<br>
<br>
Id (primary key)<br>
MRTPContactId (id of contact from table MRTPContact)<br>
Key (key from pair key =&gt; value)<br>
Value (value from pair key =&gt; value)<br>
<br>
So I want the get the list of keys used in the table.<br>
<br>
<pre class="moz-signature" cols="72">Miroslav Šulc</pre>
<br>
<br>
Alvaro Herrera napsal(a):
<blockquote cite="mid20060601135310.GB18513@surnet.cl" type="cite">
  <pre wrap="">Miroslav ?ulc wrote:
  </pre>
  <blockquote type="cite">
    <pre wrap="">Hello,

I have a table with cca 400,000 rows. The table contains column "key" of
varchar(20) type containing 10 distinct values. I want to get out what
distinct values are present in the column. I use this simple query,
which is very slow:

SELECT DISTINCT Key FROM MRTPContactValue
    </pre>
  </blockquote>
  <pre wrap=""><!---->
You could get the universe of values from the table where this is a
primary key, and use an IN clause (which apparently is more efficient
than an EXISTS in some cases, but try that too) to search for values
that exist in the MRTPContactValue table.

I assume you do have the other table, don't you?

  </pre>
</blockquote>
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