Message-ID: <47E252F8.6030008@postnewspapers.com.au>
Date: Thu, 20 Mar 2008 21:05:12 +0900
From: Craig Ringer <craig@postnewspapers.com.au>
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To: Gavin 'Beau' Baumanis <gavinb@eclinic.com.au>
Cc: Gurjeet Singh <singh.gurjeet@gmail.com>, pgsql-sql@postgresql.org,
	"A. Kretschmer" <andreas.kretschmer@schollglas.com>
Subject: Re: Select into
References: <94F93C0F-DA95-4435-B253-57C90961DF34@eclinic.com.au>
	<20080320104922.GB18935@a-kretschmer.de>
	<65937bea0803200358i290bdc87hdeca777b593b5df1@mail.gmail.com>
	<786D2B38-CE0A-41BF-9E70-4DEB22F8D9EF@eclinic.com.au>
In-Reply-To: <786D2B38-CE0A-41BF-9E70-4DEB22F8D9EF@eclinic.com.au>
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Gavin 'Beau' Baumanis wrote:
>
> The copy is inside the same table, so I don't understand why it (the 
> required query ) would require any joins.
Maybe you should use FROM clause in the update that references a 
row-valued subquery?

craig=# create table x ( id serial, val integer );
NOTICE:  CREATE TABLE will create implicit sequence "x_id_seq" for 
serial column "x.id"
CREATE TABLE

craig=# insert into x ( val ) values ( 4 ) , ( 6 ) ;
INSERT 0 2

craig=# select * from x;
 id | val
----+-----
  1 |   4
  2 |   6
(2 rows)

craig=# update x set val = foundrow.val from ( select val from x where 
id = 2 ) as foundrow where id = 1 ;
UPDATE 1

craig=# select * from x;
 id | val
----+-----
  2 |   6
  1 |   6
(2 rows)

craig=# insert into x ( val ) select generate_series(0,10000);
INSERT 0 10001

craig=# explain update x set val = foundrow.val from ( select val from x 
where id = 4123 ) as foundrow where id = 5912 ;
                               QUERY PLAN
-------------------------------------------------------------------------
 Nested Loop  (cost=0.00..16.55 rows=1 width=14)
   ->  Index Scan using x_id_idx on x  (cost=0.00..8.27 rows=1 width=10)
         Index Cond: (id = 5912)
   ->  Index Scan using x_id_idx on x  (cost=0.00..8.27 rows=1 width=4)
         Index Cond: (public.x.id = 4123)
(5 rows)

Will that do the job?

--
Craig Ringer