INDEXES

An Index:

• Is a schema object
• Can be used by the Oracle server to speed up the retrieval of rows by using a pointer.
• Can reduce disk I/O by using a rapid path access method to locate data quickly
• Is independent of the table that it indexed
• Is used and maintained automatically by the Oracle server
  

1. Unique Index : Primary Key or Unique : automatically create an index
2. NOnunique Index : User created index. ex) FOREIGN KEY

- If there is no INDEX, then a full table scan occurs.
- If you drop a table, corresponding indexes are also dropped.

Types of Indexes

1. Unique Index : The Oracle server automatically creates this index when you define a column in a table to have a PRIMARY KEY or UNIQUE key constraint.
2. Nonunique Index : This is an index that a user create.