From: Bjarke Dahl Ebert <bebert@tiscali.dk>
To: pgsql-sql@postgresql.org
Subject: Re: problematic query (for me ;-)
Date: Thu, 6 Mar 2003 02:44:47 +0100
Message-ID: <_Nx9a.112430$Hl6.10266647@news010.worldonline.dk> (raw)
References: <3E660A41.7040509@kyborg.dk>
"Kim Petersen" <kp@kyborg.dk> wrote in message
news:3E660A41.7040509@kyborg.dk...
> I'm trying to get a hint as to how i can solve this problem:
>
> i have a table:
>
> n | t
> ---+---
> 1 | 2
> 1 | 5
> 2 | 3
> 2 | 5
> 3 | 4
> 3 | 3
> (6 rows)
>
> now i want to find the pairs (n1,n2) where no t's collide - eg in this
> table it would be (1,3) and (3,1).
SELECT DISTINCT nt1.n, nt2.n FROM nt nt1, nt nt2
WHERE NOT EXISTS (
(SELECT t from nt where n=nt1.n) INTERSECT
(SELECT t from nt where n=nt2.n))
n | n
---+---
1 | 3
3 |1
(2 rows)
I'm not sure that it scales well to large datasets...
/Bjarke
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To: pgsql-sql@postgresql.org
Cc: bebert@tiscali.dk
Subject: Re: problematic query (for me ;-)
In-Reply-To: <_Nx9a.112430$Hl6.10266647@news010.worldonline.dk>
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