If I say the INTERNAL BEHAVIOR, is it more clear?
Perhaps you were confused thinking in the results.
The result of EXISTS is the same, but the implementation to produce that
result is vendor-dependent. If the implementation is slow (like requesting
all records only to know if the recordset is empty, as people did in the
client side when asking for RecordCount>0 in Delphi instead of BOF+EOF),
then we might prefer TOP. Anyway, I thought it was clear by reading the
prior posting, sorry.

C.

> -----Original Message-----
> From: Ungod [mailto:ungod@...]
> Sent: Miércoles 28 de Junio de 2000 8:11
> To: IBDI@egroups.com
> Subject: RE: [IBDI] Re: function TOP n FROM... was (Porting from...)
>
>
> excuse me? Exists is part of SQL92 semantics, if a vendor's behaviour is
> non-standard, then there's a problem with that vendors implementation.
>
> --
> Ungod (W.King)
> www.bytamin-c.com
> www.magick.tm
> I found the answer, now where'd I put that problem...
>
>
> -----Original Message-----
> From: Claudio Valderrama C. [mailto:cvalde@...]
> Sent: Wednesday, 28 June 2000 5:44 PM
> To: IBDI@egroups.com
> Subject: RE: [IBDI] Re: function TOP n FROM... was (Porting from...)
>
>
> The problem with EXISTS() is that the behavior is vendor-dependent. The db
> engine can:
> - Get all the recordset and ensure count()>0.
> - Get one record and exit immediately.
> - Other nasty tricks.
>
> So, I will ask in IB-Architect what's the implementation. Why do you think
> that TOP_1 is expensive, Helen?
>
> C.
>
> > -----Original Message-----
> > From: Helen Borrie [mailto:helebor@...]
> > Sent: Martes 27 de Junio de 2000 12:06
> > To: IBDI@egroups.com
> > Subject: Re: [IBDI] Re: function TOP n FROM... was (Porting from...)
> >
> >
> > At 02:05 PM 27-06-00 +0000, you wrote:
> >
> > >The reason why I asked about TOP N in the first place is that I use a
> > >3rd party DLL that uses TOP 1 to check if a database table is empty.
> > >
> > >This vendor prefers to do a TOP 1 rather than COUNT(*) because some
> > >databases do a full table scan to count the records. TOP 1
> > ><i>hopefully</i> prevents this.
> > >
> > > -- John
> >
> > Oh, that is so expensive! What about IF EXISTS() ?
> >
> > Helen
> >
> >
> >
> >
> >
> > >--- In IBDI@egroups.com, Ann Harrison <harrison@n...> wrote:
> > > >
> > > > >
> > > > >TOP isn't standard SQL and it's not a very sensible kind of thing
> > >to ask of
> > > > >a Client/Server database, given that the data isn't stored in any
> > >physical
> > > > >order. I'd be surprised if got anywhere near the top of anyone's
> > >list of
> > > > >"must-haves" for InterBase.
> > > >
> > > > There is one place where TOP<n> would be useful. Currently, an
> > >order
> > > > by clause causes InterBase to retrieve and sort the result set,
> > >unless
> > > > the order by terms match an index exactly and the query is simple
> > > > (single table?). In that restricted case, InterBase retrieves the
> > > > rows in index order. You probably think that index order would be
> > > > faster than sorting, but you would be wrong, in general. The one
> > >case
> > > > where walking in index order is reliably faster is when you want
> > >only
> > > > the TOP<n> rows. So TOP could be a nice hint to the optimizer.
> > > >
> > > > Ann
> > >
> > >
> >
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