IIRC, the subselect is executed only once, but using IN (...) can be slow for
large result sets because the searching in IN is just a sequential scan of
that result set.
Not sure why it'd be faster to crop of the first and last ones though..
--
Shane
On Monday 18 Feb 2002 3:42 pm, Bruce Momjian wrote:
> hubert depesz lubaczewski wrote:
> > On Mon, Feb 18, 2002 at 09:52:19AM -0500, Bruce Momjian wrote:
> > > Not that I know of.
> >
> > strange. what could lead to this results then?
> > i used to think that IN (SELECT ...) is the slowest possible way at all.
> >
> > depesz
> >
> > p.s. of course both select's use indices, and table is vacuumed
>
> I have always wondered this too. Seems IN evaluates the entire query
> while EXISTS evaluates it for each row, or at least that is how I
> understand it, so saying EXISTS is always faster may be wrong.
> Comments?
