From: A. Kretschmer <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: ordered by join? ranked aggregate? how to?
Date: Tue, 15 Sep 2009 09:49:57 +0200
Message-ID: <20090915074957.GA8046@a-kretschmer.de> (raw)
In-Reply-To: <d7867e26-d5de-4c48-bfac-d6f266b47ec6@l34g2000vba.googlegroups.com>
References: <d7867e26-d5de-4c48-bfac-d6f266b47ec6@l34g2000vba.googlegroups.com>
In response to wstrzalka :
> What I need is to join 2 tables
>
> CREATE TABLE master(
> id INT4
> );
>
>
> CREATE TABLE slave (
> master_id INT4,
> rank INT4,
> value TEXT);
>
>
> What I need is to make the query:
>
> SELECT m.id, array_agg(s.value) AS my_problematic_array
> FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id)
> GROUP BY m.id;
>
> return the 'my_problematic_array' in order specified by slave.rank
>
> As you probably can guest I don't have any idea know how to do it :/
test=*# select * from master;
id
----
1
2
(2 rows)
test=*# select * from slave;
master_id | rank | value
-----------+------+-------
1 | 5 | 5
1 | 3 | 3
1 | 7 | 7
(3 rows)
test=*#
select id, array_agg(unnest) from (
select id, unnest(my_problematic_array) from (
SELECT m.id, array_agg(s.value) AS my_problematic_array FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id) GROUP BY m.id
) foo order by 1,2
) bar group by 1;
id | array_agg
----+-----------
1 | {3,5,7}
2 | {NULL}
(2 rows)
Andreas
--
Andreas Kretschmer
Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: -> Header)
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To: pgsql-sql@postgresql.org
Cc: andreas.kretschmer@schollglas.com
Subject: Re: ordered by join? ranked aggregate? how to?
In-Reply-To: <20090915074957.GA8046@a-kretschmer.de>
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