From: | Vincent Veyron <vv(dot)lists(at)wanadoo(dot)fr> |
---|---|
To: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Optimizing query? |
Date: | 2013-01-31 14:00:30 |
Message-ID: | 1359640830.2444.29.camel@asus-1001PX.home |
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Lists: | pgsql-general |
Le jeudi 31 janvier 2013 à 11:06 +0100, Pavel Stehule a écrit :
> 2013/1/31 Vincent Veyron <vv(dot)lists(at)wanadoo(dot)fr>:
> >
> > Suppose I have a query of the form
> >
> > SELECT my_function(column_1), column_2
> > FROM my_table
> > GROUP BY my_function(column_1)
> > ORDER BY my_function(column_1);
> >
> > where my_function is a user defined function.
> >
> > How many times is the function computed?
>
> if function is stable or immutable, then once per row
>
In this post (watch for line-wrap) :
http://www.postgresql.org/message-id/CAFj8pRAdYL1-hCxH
+QSZQKHt9YnoaOiGkfX4cNc9mzUTimcs1w(at)mail(dot)gmail(dot)com
you wrote that it is usually better not to mark SQL functions (as
opposed to plpgsql functions).
So should I mark SQL functions stable/immutable if I use them in a query
like the one above, or is it unnecessary?
--
Salutations, Vincent Veyron
http://marica.fr/site/demonstration
Logiciel de gestion des contentieux juridiques et des sinistres d'assurance
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