--- In firebird-support@yahoogroups.com, Ann Harrison <aharrison@...> wrote:

>
> On Fri, Apr 13, 2012 at 12:43 PM, venussoftop <venussoftop@...> wrote:
>
> >
> >
> > --- In firebird-support@yahoogroups.com, Svein Erling Tysvær
> > <svein.erling.tysvaer@> wrote:
> > > First, I would generally recommend you to forget that it is at all
> > possible to use IN (<subselect>). Myself, I occasionally use IN (constant),
> > but hardly ever IN (<subselect>) - using EXISTS can normally replace it, is
> > sometimes faster and never slower (well, I don't know about the later
> > Firebird versions, but would expect there to still be queries that Firebird
> > doesn't convert from IN (<subselect>) to EXISTS under the hood).
> >
>
> There's a semantic difference between NOT IN and the equivalent NOT EXISTS
> having to do with NULL values and empty result sets. I've understood it
> from time to time, but this is not one of those times. So it's not
> possible to fold all IN subqueries into EXISTS subqueries. Worse, the NOT
> IN defies index optimization.
>
>
> > Somehow IN comes to my mind first, I am at an intermediate stage where I
> > am neither a beginner nor a pro with SELECTs :)
>
>
>
> Having IN come to mind is not a problem. Just train your mind to think of
> NOT IN as a programmer trap, to be avoided if at all possible.
>
>
> Good luck,
>
>
> Ann
>
>
> [Non-text portions of this message have been removed]
>

Thanks Ann.

Kind regards
Bhavbhuti