What Is Cluster in Oracle ?

A Cluster is a schema object used to store related information from multiple tables at stable physical location in a single data block.

•  we need to create a cluster with cluster column then, we need to create a index on cluster column. this index is called cluster index.
• Create the related tables and store them in a cluster by using a cluster clause.
• use the cluster clause at theend of all column definitions in cluster tables.

EX:

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create cluster personel1 (dept number(4))

size 512

storage (initial 100k next 50k);

cluster index:

==========

create index indx_personel1 on cluster personel1;

adding tables to a cluster:

====================

create table dept_10

cluster personel1(dept)

as select * from emp where deptno=10;

create table dept_20

cluster personel1(dept)

as select * from emp where deptno=20;