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Re: Need help in grouping records

From: Andreas <maps(dot)on(at)gmx(dot)net>
To: Jasen Betts <jasen(at)xnet(dot)co(dot)nz>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: Need help in grouping records
Date: 2012-05-20 09:08:25
Message-ID: 4FB8B489.3050701@gmx.net (view raw or flat)
Thread:
Lists: pgsql-sql
Am 20.05.2012 05:04, schrieb Jasen Betts:
> On 2012-05-19, Andreas<maps(dot)on(at)gmx(dot)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
>
>
>
Thanks   :)
Thats by far more elegant as my approach with arrays I figured out in 
the meantime.

I changed rank() to dense_rank() in your solution.

Functionally the 1st line does allready all the magic, though.

Great   :)


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