Re: question about sequences.

Jim Kennedy wrote:

> Daniel,
> Sure we don't know what the interviewer was thinking, but this the type of
> question that one might use to dig for experience and problem solving. It
> is likely the sequence question alone is fairly simple and straightforward
> (one would hope), but by combining it with this "odd" behavior (Hmm, got 2
> rows back from dual.) The interviewer is asking both about sequences, what
> dual is, and why might it be acting unusual.(have 2 rows) It is the type of
> thing that would happen in real life (some bozo did an insert into dual and
> now it has 2 rows, and is creating all sorts of havoc.)
> Jim
> "DA Morgan" <damorgan_at_exesolutions.com> wrote in message
> news:3E4FD982.EDE9B0B0_at_exesolutions.com...
> > Jim Kennedy wrote:
> >
> > > I think the question was aimed at finding out that someone had added a
> row
> > > to dual and that will cause problems with applications that use dual
> > > expecting 1 row.
> > > Jim
> > >
> > > --
> > > Replace part of the email address: kennedy-down_with_spammers_at_attbi.com
> > > with family. Remove the negative part, keep the minus sign. You can
> figure
> > > it out.
> > > <Kenneth Koenraadt> wrote in message
> > > news:3e4f8b9d.629164_at_news.inet.tele.dk...
> > > > On Sat, 15 Feb 2003 18:17:04 GMT, "Ryan" <rgaffuri_at_cox.net> wrote:
> > > >
> > > > >I got a trick question in an interview and I dont know if what I said
> was
> > > > >write. It was a written exam so I couldnt ask.
> > > > >
> > > > >Someone does
> > > > >
> > > > >select sequence.nextval
> > > > > from dual;
> > > > >
> > > > >you get two sequence numbers back. All I could think of was that
> someone
> > > > >inserted a second row into dual.
> > > > >
> > > > >Could any other reason lead to two sequence numbers being returned?
> > > > >
> > > > >
> > > >
> > > > Hi Ryan,
> > > >
> > > > Maybe the question was just awkwardly asked. I guess they wanted to
> > > > test if you knew about both sequence.NEXTVAL and sequence.CURRVAL :
> > > >
> > > > Nextval is returned from the statement. No doubt. And if you
> > > > afterwards do :
> > > >
> > > > select sequence.currval from dual;
> > > >
> > > > You get the same value again. In that sense, you can say that you get
> > > > 2 values at your service, *because* :
> > > >
> > > > If you start a user session and have a sequence myseq and issue :
> > > >
> > > > select myseq.currval from dual;
> > > >
> > > > You get ORA-08002: Sequence MYSEQ.CURRVAL not yet defined.....
> > > >
> > > > You have to invoke NEXTVAL by *first* calling
> > > >
> > > > select myseq.nextval from dual;
> > > >
> > > > and *then* you can do ;
> > > >
> > > > select myseq.currval from dual;
> > > >
> > > > So "select sequence.nextval from dual" does, make another value
> > > > avilable : sequence.currval.
> > > >
> > > > Interviewers trying to make tricky questions, are often tricking
> > > > themselves instead....
> > > >
> > > > - Kenneth Koenraadt
> > > >
> > > >
> > > >
> >
> > As opposed to SELECT COUNT(*) FROM dual;?
> >
> > The question is reasonable as a way of understanding someone's
> understanding of
> > dual and how sequences work. Trying to psychoanalyze those that put
> together the
> > questions may not lead to a lot of clarity as we'll likely never know why
> any
> > question ends up on one of these things.
> >
> > What I find more amazing is the questions and answers (especially on the
> OCP)
> > that are clearly incorrect.
> >
> > Daniel Morgan
> >

Hope you didn't misunderstand ... I think it is a great question and plan to add it to my repetoire for just the reasons you cite.

Daniel Morgan Received on Sun Feb 16 2003 - 15:58:05 CST