Re: Optimizing query?

2013/1/31 Vincent Veyron <vv(dot)lists(at)wanadoo(dot)fr>:
> 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?
>

It should not be marked

Regards

Pavel

>
> --
> Salutations, Vincent Veyron
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