Re: Optimizing query?

Le jeudi 31 janvier 2013 à 11:06 +0100, Pavel Stehule a écrit :
> 2013/1/31 Vincent Veyron <vv.lists@wanadoo.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@mail.gmail.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
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