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Date: Mon, 17 Feb 2014 14:12:41 -0800 (PST)
From: David Johnston <polobo@yahoo.com>
To: pgsql-sql@postgresql.org
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Subject: Re: include ids in query grouped by multipe values
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Karsten-3-2 wrote
> select IDone, IDtwo, max(sale) as maxsale FROM TableA group by IDone,
> IDtwo;
>  
> But it would want to also select the id column ( and all other additonal
> 20
> columns of TabelA not shown above) and need that there is only one record
> returned for each IDone - IDtwo combination. I tried 
>  
> SELECT a.id, a.IDone, a.IDtwo, a.sale FROM TableA a
> inner join ( select IDone, IDtwo, max(sale) as maxsale FROM TableA group
> by
> IDone, IDtwo ) b
> on a.IDone = b.IDone and b.IDtwo = b.IDtwo  
> and a.sale = b.maxsale;
>  

[Not Tested]

SELECT b.IDone, b.IDtwo, b.sale, array_agg(a) AS matching_on_tableA
FROM TableA a
NATURAL JOIN ( SELECT IDone, IDtwo, max(sale) AS sale FROM TableA GROUP BY
1, 2 ) b
GROUP BY 1, 2, 3;

In this solution you simply save the entire tableA record, as a composite
typed column, into an array so that you now have a single row for each
"IDone, IDtwo, (max)sale" combination - which you omitted in the description
above - but can still access to relevant matching rows using the array.  Add
"ORDER BY" - e.g., array_agg(...ORDER BY) - to setup a desired sort order. 
You can do something like (against, not tested):

SELECT IDone, IDtwo, sale, (array_agg[0]).* AS row_from_tablea FROM <the
above query>

to get to the relevant data in the array.

David J.




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