Re: index

From: Evan Keel <evankeel_at_sbcglobal.net>
Date: Mon, 28 Jul 2008 17:52:16 -0400
Message-ID: <dbrjk.6804$cn7.4273_at_flpi145.ffdc.sbc.com>


"Brian Selzer" <brian_at_selzer-software.com> wrote in message news:%Vpjk.34162$ZE5.24396_at_nlpi061.nbdc.sbc.com...
>
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:488de63f$0$4041$9a566e8b_at_news.aliant.net...
> > aarklon_at_gmail.com wrote:
> >
> >> Hi all,
> >>
> >> I read the following in a book
> >>
> >> 1) we can have several non clustered indexes on a table , but we can
> >> have only one clustered index per table
> >>
> >> 2) index on the primary key can be clustered or non clustered
> >>
> >> now my question is
> >>
> >> 1) to what extent these statements are true ?
> >
> > To the extent the statements accurately describe the physical
> > implementation of a particular dbms, they are true.
> >
> > Theoretically, one can have multiple clustered indexes at the cost of
> > duplicating the data, which of course incurs a cost. Vendors typically
> > assUme nobody would ever want to incur that cost.
>
> This is bunk. Badour is an idiot. Where there is a clustered index, that
> index /is/ the table--that is, the table is physically stored using
whatever
> data structure is in use for indexes--probably b-trees. A table that does
> not have a clustered index, on the other hand, is physically stored as a
> heap. The leaf nodes of a clustered index /are/ the rows of the table.
The
> leaf nodes of a non-clustered index are either pointers to rows on the
heap
> (where there is no clustered index) or clustered index keys (along with a
> uniquifier [I didn't coin the term, so don't blame me] if the clustered
> index isn't also a unique index). Although it is possible to have
multiple
> indexes that cover the entire heading, that is not the same thing as
having
> multiple clustered indexes.
>
Though I agree with you, you are not a very nice person. Why the invective re: Badour? Received on Mon Jul 28 2008 - 23:52:16 CEST

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