Re: About indexes and clusters
Date: Fri, 7 Nov 2003 11:58:12 -0500
Message-ID: <w7GdnTWHirfZUjaiRVn-sw_at_golden.net>
"Juan Pardillos" <sicotom_at_eresmas.com> wrote in message
news:6278687.0311070834.131981e4_at_posting.google.com...
> Hi everybody,
>
> I have some doubts about these topics. I hope you can help me:
>
> a) I have read that some queries can be solved by just querying the
> indexes, without actually retrieving data. I don't see this point.
> Could anyone give me an example?
A dbms can sometimes answer queries from an index without accessing the heap, which is a very different thing. The dbms accesses the data from the index which contains data about the key or the indexed values.
> b) Why it is possible to define an index over several attributes (and
> the file is ordered taking all of them into account, in the order
> these attributes are specified), but it is only possible to define a
> cluster over a single attribute?
Arbitrary vendor limitation. Received on Fri Nov 07 2003 - 17:58:12 CET