Re: BUG #3910: Incorrect behavior of UPDATE statement on tables with constraints UNIQUE/PRIMARY KEY

[David Fetter <david(at)fetter(dot)org>]

On Tue, Jan 29, 2008 at 09:45:28AM +0000, Dmitry Afanasiev wrote:
> 
> The following bug has been logged online:
> 
> Bug reference:      3910
> Logged by:          Dmitry Afanasiev
> Email address:      KOT(at)MATPOCKuH(dot)Ru
> PostgreSQL version: 7.4.19
> Operating system:   FreeBSD 7.0 / 5.5
> Description:        Incorrect behavior of UPDATE statement on tables with
> constraints UNIQUE/PRIMARY KEY
> Details: 
> 
> Constraints must be checked AFTER updating ALL of rows, but really after
> every row.
> For illustrate try this simple sql script:
> CREATE TABLE n(n INTEGER PRIMARY KEY);
> INSERT INTO n VALUES(1);
> INSERT INTO n VALUES(2);
> INSERT INTO n VALUES(3);
> UPDATE n SET n = n + 1;
> SELECT * FROM n;
> DROP TABLE n;
> 
> On UPDATE psql says about violation UNIQUE constraint and does't update
> anything.
> For example, in Oracle all works propertly, and result of SELECT is:
> SQL> select * from n;   
> 
>          N
> ----------
>          2
>          3
>          4

You can get around this by doing:

UPDATE t
SET n=t.n+1
FROM (
    SELECT n FROM t ORDER BY n DESC
) t1
WHERE t1.n=t.n;

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

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