Re: Newbie question on indexes

From: J L Joslin <jjoslin_at_us.oracle.com>
Date: 1997/10/19
Message-ID: <344b76c9.1331284@news-s01.ca.us.ibm.net>#1/1

On 18 Oct 1997 16:56:44 GMT, steve18888_at_aol.com (Steve18888) wrote:

>What exactly do indexes do and why do I want to use them? From my reading I

> gather that it improves query performances somehow. Digging through my manuals
> tells me how to create indexes, but can't find anything on the strategy behind
> it. Also, if I create an index, are there any other settings that I need to
> make, or do the indexes get used automatically somehow? Thanks - SS

Generally speaking, indexes contain ordered lists of the values for specified columns and a pointer directly to the referenced row. When tables do not have indexes, Oracle has no choice but to scan the entire table from beginning to end to resolve queries. When indexes are in place, an operation called an INDEX RANGE SCAN or INDEX SCAN (depending upon the where clause) is used to resolve the query The INDEX <RANGE> SCAN operation retrieves pointers to required rows and uses the pointers to retrieve the rows from the target table(s).

I'd recommend a copy of "Oracle: A Beginner's Guide". It will explain many of these concepts in plain english. It is well known as a good introduction to the basics of Oracle.

Regards,

Jim Joslin, Principal Consultant
Oracle Consulting Services - Florida Technology Practice

The opinions expressed herein are mine and do not represent those of Oracle Corporation. Received on Sun Oct 19 1997 - 00:00:00 CDT