From: Miroslav Šulc <miroslav.sulc@startnet.cz>
To: pgsql-sql@postgresql.org
Subject: Re: SELECT DISTINCT too slow
Date: Thu, 01 Jun 2006 16:49:54 +0200
Message-ID: <447EFE92.2070509@startnet.cz> (raw)
In-Reply-To: <20060601135310.GB18513@surnet.cl>
References: <447EEAF1.7040305@startnet.cz>
<20060601135310.GB18513@surnet.cl>
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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Subject: Re: SELECT DISTINCT too slow
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