Re: Seq scan on zero-parameters function

Tomasz Myrta said:
> Dnia 2004-02-06 08:19, U¿ytkownik Octavio Alvarez napisa³:
>> In each couple, the first one has a WHERE field = function()
>> condition, just like the second one, but in the form WHERE field =
>> (SELECT function()). In my opinion, both should have the same execution
>> plan, as the function has no parameters and, therefore, is constant.
>
> Nope.
>
> What would you say about function without params returning timeofday()?
> Is it constant?

No... :-P ;-)

> If you are sure, that your function returns constant value - declare it
> as IMMUTABLE. (look at CREATE FUNCTION documentation)

Thanks for the hint.

In fact, my current_period_id() is based on time, but it should be
constant along the query execution. I mean, I don't want some records
filtered with some values and other with other values... I'll have an
uncongruent recordset.

Say SELECT [field-list] FROM [complex-join] WHERE sec = datepart('second',
now()); Now suppose the query takes always more than 1 second because of
the complex-join or whatever reason: I will naver have a congruent
recordset.

IMMUTABLE wouldn't help here, only wrapping the function in a subquery. Is
this expected behavior? Is this standards compliant (if it can be
qualified as such)?

Octavio.

--
Octavio Alvarez.
E-mail: alvarezp(at)alvarezp(dot)ods(dot)org(dot)

Agradezco que sus correos sean enviados siempre a esta dirección.