Difference between Cluster and Non-cluster index?
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Answer Posted / hannan
First, you must understand what a cluster is in Oracle.
A cluster is simply a method for storing more then 1 table
on the same block. Normally
-- a block contains data for exactly 1 table. In a cluster
-- you have data from many
tables sharing the same block.
For example -- if you join the data from EMP and DEPT by
DEPTNO frequently -- you might
consider clustering this data by DEPTNO. In that fashion
all of the rows from EMP for
deptno=10 and the row in DEPT for deptno=10 will reside on
the same exact block (one IO
to get all of the data instead of some IO's to EMP and DEPT).
In order to organize data in such an object, we create a
cluster KEY -- deptno in our
above example. We must index this cluster key. This index
on deptno in the cluster is
called a CLUSTER INDEX and is used to locate the blocks that
contain data about deptno=10
| Is This Answer Correct ? | 21 Yes | 4 No |
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