Re: [PERFORM] Big IN() clauses etc : feature proposal

Hi, PFC,

PFC wrote:

>     You need to do some processing to know how many rows the function
> would  return.
>     Often, this processing will be repeated in the function itself.
>     Sometimes it's very simple (ie. the function will RETURN NEXT each
> element in an array, you know the array length...)
>     Sometimes, for functions returning few rows, it might be faster to
> compute the entire result set in the cost estimator.

I know, but we only have to estmiate the number of rows to give a hint
to the query planner, so we can use lots of simplifications.

E. G. for generate_series we return ($2-$1)/$3, and for some functions
even constant estimates will be good enough.

>     - please execute me and store my results in a temporary storage,
> count  the rows returned, and plan the outer query accordingly

That's an interesting idea.

Markus


--
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org