9. index and index organized table

What is and Index?
• It is a data structure associated with a table
that enables fast searching of data.
• Indexes are schema objects that are logically
and physically independent of the data in the
objects with which they are associated.
• Indexes are structures stored in the database
that users manage using SQL statements.

What is an Index?
• Primary and unique keys automatically have
indexes, but create an index on a foreign key.
• Index must be created on the most frequently
columns in the table.
• Oracle Database does not index table rows in
which all key columns are null.

What is an Index?
• An index contains a collection of keys and
pointers.
– Keys are values built from one or more columns in
the table
– Pointer stores the address of the location where a
data block stored in the memory.

What is an Index?
• Composite Index
– Index based on one or more columns is called
composite index.
– Multiple indexes can exist for the same table if the
permutation of columns differs for each index.

What is an Index?
• Unique Indexes
– Unique indexes guarantee that no two rows of a
table have duplicate values in the key column or
columns.
– The data is sorted only by key.
• Non Unique Indexes
– Nonunique indexes permit duplicates values in the
indexed column or columns.
– The rowid is included in the key in sorted order

Types of Indexes
• B-tree Indexes
• Bitwise Indexes
• Function Based Indexes
• ALL_INDEXES view is used to list all the
indexes details.

Types of Indexes
• B-tree Indexes
– These indexes are the standard (NORMAL) index
type.
– They are excellent for primary key and highly-
selective indexes.
– Order list of values divided into ranges.
CREATE INDEX indexname
ON table_name(column)list);

Types of Indexes
• Bitmap Index
– In a bitmap index, the database stores a bitmap
for each index key.
– Used for the columns when the number of distinct
values is small compared to the number of table
rows.
CREATE BITMAP INDEX index_name
ON table_name (column_name);
Value Row 1 Row 2 Row 3 Row 4 Row 5 Row 6 Row 7 Row 8
Male 1 1 0 1 0 1 0 1
Female 0 0 1 0 1 0 1 0

Function Based Index
• Function Based Index
– A function-based index computes the value of a
function or expression involving one or more
columns and stores it in the index.
– A function-based index can be either a B-tree or a
bitmap index.
CREATE INDEX index_name
ON tablename (expression(s) [, column_list]);

Function Based Index
• Function Based Index
– The database only uses the function-based index
when the function is included in a query not at
INSERT or UPDATE statement.

Index Organised Tables
• An index-organized table is a table stored in a
variation of a B-tree index structure.
• In an index-organized table, rows are stored in
an index defined on the primary key for the
table.
• An index-organized table stores all data in the
same structure and does not need to store the
rowid.

Heap Organised vs Index Organised Tables
• In heap organised table,
– the rowid uniquely identifies a row.
– Primary key constraint may optionally be defined.
• In Index organised table,
– Primary key uniquely identifies a row.
– Primary key constraint must be defined.

• In heap organised table,
– Individual rows may be accessed directly by rowid.
• In Index organised table
– Access to individual rows may be achieved
indirectly by primary

• In heap organised table, can contain a column
of the LONG data type and LOB data types.
• In Index organised table, can contain LOB
columns but not LONG columns.

• Heap organised Table

• Indexed organised Table

9. index and index organized table

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