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From: "Bjarke Dahl Ebert" <bebert@tiscali.dk>
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References: <3E660A41.7040509@kyborg.dk>
Subject: Re: problematic query (for me ;-)
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Date: Thu, 6 Mar 2003 02:44:47 +0100
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"Kim Petersen" <kp@kyborg.dk> wrote in message
news:3E660A41.7040509@kyborg.dk...
> I'm trying to get a hint as to how i can solve this problem:
>
> i have a table:
>
>   n | t
> ---+---
>   1 | 2
>   1 | 5
>   2 | 3
>   2 | 5
>   3 | 4
>   3 | 3
> (6 rows)
>
> now i want to find the pairs (n1,n2) where no t's collide - eg in this
> table it would be (1,3) and (3,1).

SELECT DISTINCT nt1.n, nt2.n FROM nt nt1, nt nt2
WHERE NOT EXISTS (
    (SELECT t from nt where n=nt1.n) INTERSECT
    (SELECT t from nt where n=nt2.n))

 n | n
---+---
 1 | 3
 3 |1
(2 rows)

I'm not sure that it scales well to large datasets...

/Bjarke