Message-ID: <45D9E4C4.1080304@planit.com.br>
Date: Mon, 19 Feb 2007 15:56:20 -0200
From: "Luiz K. Matsumura" <luiz@planit.com.br>
Organization: Plan IT Tecnologia =?ISO-8859-1?Q?Inform=E1tica_Ltda=2E?=
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To: Salman Tahir <salmantahir1@gmail.com>
CC: pgsql-sql@postgresql.org
References: <2049e51a0702190858n6932461dgc294d05b035aad53@mail.gmail.com>
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Subject: Re: cartesian product

Hi, Salman

Maybe this isn't so much elegant, but works:

SELECT p1.sequence as sequence1, p2.sequence as sequence2
FROM potential_pairs p1, potential_pairs p2
WHERE p1.sequence <= p2.sequence

Hope this helps


Salman Tahir wrote:
> Hi,
>
> I have a query regarding an SQL statement I'm trying to execute. I
> have the following table:
>
> sequence
> -------------+
> AK
> AKCMK
> CMKA
>
> I execute the following statement (Cartesian product):
>
> SELECT p1.sequence as sequence1, p2.sequence as sequence2
> FROM potential_pairs p1, potential_pairs p2
>
> which gives me:
>
> sequence1 | sequence2
> ----------------+--------------
> AK           | AK
>  AK           | AKCMK
>  AK           | CMKA
>  AKCMK    | AK
>  AKCMK    | AKCMK
>  AKCMK    | CMKA
>  CMKA      | AK
>  CMKA      | AKCMK
>  CMKA      | CMKA
> (9 rows)
>
> I want to eliminate duplicates and by duplicate I mean a tuple such as
> {AK, CMKA} should be regarded as the same as {CMKA, AK}. So I would
> like the following result:
>
> sequence1 | sequence2
> ----------------+--------------
> AK           | AK
>  AK           | AKCMK
>  AK           | CMKA
>  AKCMK    | AKCMK
>  AKCMK    | CMKA
>  CMKA      | CMKA
>
> Any help would be appreciated.
>
> - Salman
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>       choose an index scan if your joining column's datatypes do not
>       match
>
>

-- 
Luiz K. Matsumura
Plan IT Tecnologia Informática Ltda.