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Tip of the Day
Language: Enterprise
Expertise: Advanced
May 16, 2000

Faster Data Access Using Index-Organized Tables

If you have a table whose columns always are queried together, maybe you should store them as an index-organized table (IOT). An IOT is indexed on one or more columns and all the table data is maintained as a B*tree index. Any manipulation of table data updates the index. The data rows are built on the primary key for the table.

IOTs provide faster data access to queries that involve exact matches or range searches or both. Also, the storage requirement gets reduced because, unlike normal tables, IOTs don't require separate indexes.

A simple statement for creating an IOT is:

 create table table_name ( col1 number primary key, col2 varchar2(20))
	 ORGANIZATION INDEX;
However, IOTs also have some restrictions. They do not support Distribution or Replication, and cannot have UNIQUE constraints on the table.
Jayanta Sengupta
 
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