To: pgsql-sql@postgresql.org
From: Jasen Betts <jasen@xnet.co.nz>
Subject: Re: Need help in grouping records
Date: 20 May 2012 03:04:12 GMT
Organization: Dis (not Dat) Organisation
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Message-ID: <jp9mvc$qmu$1@reversiblemaps.ath.cx>
References: <4FB7EEC6.1030004@gmx.net>
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On 2012-05-19, Andreas <maps.on@gmx.net> wrote:
> Hi,
>
> I'm trying to fight against double entries in tables.
> I got as far as I can find similar records with trigram string matching.
> If I do this with a table compared to itself I get something like this:
>
> id_a, id_b
> 3,   5
> 3,   7
> 5,   3
> 5,   7
> 7,   3
> 7,   5
> 11,   13
> 13,   11
>
> so the records with the IDs 3, 5, 7 and 11, 13 are similar enough to 
> form a group.
>
> How would I get a list of record-IDs with a group-ID like this
>
> record_id, group_id
> 3,   1
> 5,   1
> 7,   1
> 11,   2
> 13,   2
>
> Is there a way to get this by SQL ?


  select id_a,min(least(id_a,id_b)) from SOMETHING group by id_a

close enough?

or this: ?

  select id_a, rank() over order by g  from 
  ( select id_a,min(least(id_a,id_b)) as g from SOMETHING group by id_a ) as foo


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