what are oracle indexs?

[HPADM]

Hi!
I'm learning now something about oracle and I would like to know what are oracle index.
thank you

[Christian Gebhardt]

Hi

Very short answer for a complex theme:

Indexes are structures in the database to find data much faster than without it.
If you are using indexes (and you have to) you always are in a dilemma:
Indexes are necessary but need space (a lot) and cpu

Chris

[Bala_8 · Accepted solution]

hi,

An index is an optional structure associated with tables and clusters, which you can
create explicitly to speed SQL statement execution on a table. Just as the index in
a book which helps you locate information faster than if there were no index, an
Oracle index provides a faster access path to table data.
Oracle provides several indexing schemes, which provide complementary performance functionality: B*-tree indexes (currently the most common), B*-tree cluster indexes, hash cluster indexes, reverse key indexes, and bitmap indexes.
Oracle also provides support for function-based indexes and domain indexes
specific to an application or cartridge.
The absence or presence of an index does not require a change in the wording of
any SQL statement. An index merely offers a fast access path to the data; it affects
only the speed of execution. Given a data value that has been indexed, the index
points directly to the location of the rows containing that value. Indexes are logically and physically independent of the data in the associated table.
You can create or drop an index any time without affecting the base tables or other
indexes. If you drop an index, all applications continue to work; however, access to previously indexed data might be slower. Indexes, being independent structures,
require storage space.

cheers
-bala-

[HPADM]

Thank you very much, might I ask something about data dictionary?
Only to know what they are

[Christian Gebhardt]

Data Dictionary is the intern structure from oracle with tables, views, ...

So for example the view "v$database" shows you something about your database.

You can list this objects with:
select * from dict;
and a description of the columns of these objects with:
select * from dict_columns;

Chris

[T G Manikandan]

Data dictionary consists of tables and views which are stored in the system tablespace and has all the information regarding the database like the storage,structure,schema objects,users,etc.

You can get all information of the Oracle data dictionary using the static views and v$ views (dynamic).

For example you can use

select * from v$database;

This is stored in the data dictionary.This will give the information regarding the database name ,version,etc..

Just check this doc

http://www.vi.unizh.ch/oracle8i_816/onlinedocu/doc/server.816/a76961/toc.htm


Thanks

[HPADM]

What are schema objects?
I know that oracle store data logically in tablespace and physically in datafiles associated with the corresponding tablespace.
I know a little about block, extent and segment.
Is it possible for me to understand something about schema objects?

[T G Manikandan]

//*
A schema is a collection of database objects that are available to a user.
Schema objects are the logical structures that directly refer to the database's data.
Schema objects include such structures as tables, views, sequences, stored procedures, synonyms, indexes, clusters, and database links.
*//

[Jean-Luc Oudart]

Hi

looks like you need some oracle training and at least a good book to start with

cf. the osborne editions (oracle press)
http://shop.osborne.com/cgi-bin/oraclepress/

or O'Reill
http://www.oreilly.com/

Jean-Luc