Re: Index optimization ?

On Sun, 2005-01-16 at 17:45 +0100, Bo Lorentsen wrote:
> Ragnar Hafstað wrote:
> >when a volatile function is used thus:
> >  SELECT * FROM mytable WHERE col=myvolatilefunc();
> >the planner must call the function once per table row, and assume
> >possibly different return values each time, so an indexscan will
> >not improve timings.
> >
> >
> Why not use the index scan for every row, is this a "limit" in the
> planner ? I think there is something in the planner I don't understand :-)

the planner will just use the plan it estimates will be fastest.
because of how indexscans work in postgresql, in this case it would be
slower than a tablescan (assuming the function really is volatile)

gnari