Re: cartesian product

On Mon, 2007-02-19 at 10:58, 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
>

SELECT p1.sequence as sequence1, p2.sequence as sequence2 FROM
potential_pairs p1, join potential_pairs p2 on
(p1.sequence<>p2.sequence) where sequence1 > sequence2