Types of Indexes:
Oracle
Database provides several indexing schemes, which provide complementary
performance functionality. The indexes can be categorized as follows:
B-tree
indexes
These indexes are the standard index type. They are excellent for primary key
and highly-selective indexes. Used as concatenated indexes, B-tree indexes can
retrieve data sorted by the indexed columns. B-tree indexes have the following
subtypes:
Index-organized
tables
An index-organized table differs from a heap-organized because the data is
itself the index. See “Overview of Index-Organized Tables”.
Reverse
key indexes
In this type of index, the bytes of the index key are reversed, for example,
103 is stored as 301. The reversal of bytes spreads out inserts into the index
over many blocks. See “Reverse Key Indexes”.
Descending
indexes
This type of index stores data on a particular column or columns in descending
order. See “Ascending and Descending Indexes”.
B-tree
cluster indexes
This type of index is used to index a table cluster key. Instead of pointing to
a row, the key points to the block that contains rows related to the cluster
key. See “Overview of Indexed Clusters”.
Bitmap
and bitmap join indexes
In a bitmap index, an index entry uses a bitmap to point to multiple rows. In
contrast, a B-tree index entry points to a single row. A bitmap join index is a
bitmap index for the join of two or more tables. See “Bitmap Indexes”.
Function-based
indexes
This type of index includes columns that are either transformed by a function,
such as the UPPER function, or included in an expression. B-tree or bitmap
indexes can be function-based. See “Function-Based Indexes”.
Application
domain indexes
This type of index is created by a user for data in an application-specific
domain. The physical index need not use a traditional index structure and can
be stored either in the Oracle database as tables or externally as a file. See
“Application Domain Indexes”.”
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