combine multiple row values in to one row

On Tue, 7 Jul 2009 01:59:35 +0430
Lee Harr <missive@hotmail.com> wrote:

Hi;

I'm looking for a way to do this:

# select idn, magic() as codes FROM tbl;
idn | codes
-----+------
1 | A
2 | B, C
3 | A, C, E
(3 rows)

Right now, I use plpgsql functions, but each time I do it
I have to rewrite the function to customize it.

Is there a generic way to do this? An aggregate maybe?

array_accum
http://www.postgresql.org/docs/8.2/static/xaggr.html
?

--
Ivan Sergio Borgonovo
http://www.webthatworks.it

Try this.

select idn,
array_to_string(array(select code from tbl t2 where
t2.idn = t1.idn order by code), ', ') as codes
from tbl t1
group by idn
order by idn

Matthew Hartman
Programmer/Analyst
Information Management, ICP
Kingston General Hospital
(613) 549-6666 x4294

-----Original Message-----
From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-
owner@postgresql.org] On Behalf Of Lee Harr
Sent: Monday, July 06, 2009 5:30 PM
To: pgsql-general@postgresql.org
Subject: [GENERAL] combine multiple row values in to one row

Hi;

I'm looking for a way to do this:

# \d tbl
Table "public.tbl"
Column | Type | Modifiers
--------+---------+-----------
idn | integer |
code | text |
# SELECT * FROM tbl;
idn | code
-----+------
1 | A
2 | B
2 | C
3 | A
3 | C
3 | E
(6 rows)
# select idn, magic() as codes FROM tbl;
idn | codes
-----+------
1 | A
2 | B, C
3 | A, C, E
(3 rows)

Right now, I use plpgsql functions, but each time I do it
I have to rewrite the function to customize it.

Is there a generic way to do this? An aggregate maybe?

Thanks for any help.

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.now.

On Tue, Jul 07, 2009 at 01:59:35AM +0430, Lee Harr wrote:

Hi;

I'm looking for a way to do this:

# \d tbl
Table "public.tbl"
Column | Type | Modifiers
--------+---------+-----------
idn | integer |
code | text |
# SELECT * FROM tbl;
idn | code
-----+------
1 | A
2 | B
2 | C
3 | A
3 | C
3 | E
(6 rows)
# select idn, magic() as codes FROM tbl;
idn | codes
-----+------
1 | A
2 | B, C
3 | A, C, E
(3 rows)

Right now, I use plpgsql functions, but each time I do it
I have to rewrite the function to customize it.

Is there a generic way to do this? An aggregate maybe?

The aggregate is called array_agg() and it's in 8.4. You can then
wrap array_to_string() around it and get pretty formatting, as in:

SELECT idn, array_to_string(array_agg(code),', ') AS codes FROM tbl;

If you're not on 8.4 yet, you can create a similar aggregate with
CREATE AGGREGATE.

Cheers,
David.
--
David Fetter <david@fetter.org> http://fetter.org/
Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter
Skype: davidfetter XMPP: david.fetter@gmail.com

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On Tue, Jul 07, 2009 at 08:40:06AM -0700, David Fetter wrote:

On Tue, Jul 07, 2009 at 01:59:35AM +0430, Lee Harr wrote:

Is there a generic way to do this? An aggregate maybe?

The aggregate is called array_agg() and it's in 8.4. You can then
wrap array_to_string() around it and get pretty formatting, as in:

SELECT idn, array_to_string(array_agg(code),', ') AS codes FROM tbl;

Oops. That should read:

SELECT
idn,
array_to_string(array_agg(code),', ') AS codes
FROM tbl
GROUP BY idn; /* gotta group by :) */

Cheers,
David.
--
David Fetter <david@fetter.org> http://fetter.org/
Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter
Skype: davidfetter XMPP: david.fetter@gmail.com

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate