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 10:03:08 |
Message-ID: | 1359626588.2444.18.camel@asus-1001PX.home |
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Thread: | |
Lists: | pgsql-general |
Le jeudi 31 janvier 2013 à 09:49 +0100, Pavel Stehule a écrit :
> any join where result is related to some function result can be very
> slow, because estimation will be out and any repeated function
> evaluation is just expensive.
>
Hi Pavel,
Thank you for the correction. Since we're at it, I have a question
regarding functions in a query :
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?
--
Salutations, Vincent Veyron
http://marica.fr/site/demonstration
Logiciel de gestion des contentieux juridiques et des sinistres d'assurance
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