Beginer trying to understand index

Question

Hello,
I have created a table GIRLS with following details:
SQL> desc girls;
Name Null? Type
EMPNO NUMBER
NAME VARCHAR2(50)
SQL>select count(*) from girls;
COUNT(*)
1959
i created index using SQL> create index girl_name_idx on girls(name);
when i query SQL> select * from girls, I am seeing the names being displayed in same order similar to that of the names being created without index.
If my understanding is wrong,can someone explain the use of index with clear example.I also dont understand how the index helps me in speed up access to the rows.
Your help is highly appreciated.

Answer 1

I am seeing the names being displayed in same order similar to that of the names being created without index.Index has nothing to do with in what order your selected data is being returned.
If you need ordered data, then you'll (always) need an ORDER BY.
( http://tkyte.blogspot.com/2005/08/order-in-court.html )
Indexes are meant for speeding up SQL statement execution:
http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/schema.htm#CNCPT811
http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/data_acc.htm#PFGRF004
I suggest you start reading the Oracle Documentation, do some quick searches on keywords of your specific interest.
Start with the Concepts.
http://www.oracle.com/pls/db102/homepage
http://www.oracle.com/pls/db112/homepage
You'll find good explanations and examples.