Re: update only if single row

----- Original Message -----
From: "Leonid P. Klemjatsionok" <kl@84105.aanet.ru>
To: <pgsql-sql@postgreSQL.org>
Sent: Friday, April 07, 2000 8:28 AM
Subject: Re: [SQL] update only if single row


> Hi
>
> FB> select * from contact where email ~* 'rvro';
> FB> if I get a single row in the result then I enter:
> FB> update contact set bounce=1 where  email ~* 'rvro';
>
> FB> Can I combine this into a single SQL statement with the following
> FB> requirements:
> FB> 1) the update is only performed if a single row is selected
> FB> 2) I only enter the selection string ('rvro' in this case) once in the
> FB> command?
>
> Assume that pk is PRIMARY KEY (or UNIQUE attribute) of relation contact.
>
> UPDATE contact SET bounce = 1 WHERE email ~* 'rvro' AND NOT email IN
>  (SELECT c1.email FROM contact c1, contact c2
>   WHERE c1.pk != c2.pk AND c1.email = c2.email);


Surely this is not the same thing at all? This potentially updates several
rows, where there are several non-identical email addresses which all
contain rvro. The original two querys only update the row where there is
only one email address which contains rvro.

Yours,
Moray

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Moray.McConnachie@computing-services.oxford.ac.uk