Types Of Indexes In Oracle

• Index is an Object in Oracle. 
• It is a Performance Optimization Technique
• It speed up or increase the performance of the Query Execution.
• Index is creating automatically on Primary key and Unique Key.
• No need to create index for primary and unique keys columns.
• Most important thing is "we are creating the Index on frequently using COLUMNS in WHERE Condition of SQL Query ".
• Indexes are two types      1) B-Tree Index           2) Bitmap Index.

B-Tree Index

• B-Tree Indexes are using in OLTP Systems generally.
• It is used for high cardinality columns when we have too many distinct columns.
• it is  usually using in DB servers.
• B-tree indexes upadates on Key Value has relatively inexpensive.
• B-Tree index can not index  the NULL Values.

        Types of B-tree Index.
                   1)Normal Index 

                   2)Composite Index

                   3)Functional Index 

                   4)Unique Index

Bitmap Index

• Bitmap Indexes are using in OLAP Systems generally
• It is used for low cardinality columns  when we have repeated columns.
• It is usually using in DWH (Dta Warehousing Systems.
• Bitmap index has more Expensive
• Bitmap index can index  the NULL values.