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Reverse Index Creation Syntax

CREATE INDEX index_name ON table_name
  (column_list) REVERSE;

CREATE INDEX   Required keywords.
index_name   Unique name for the index.
ON   Required keyword.
table_name   The unique name of the table the index will be based on.
column_list   A list of columns whose values will make up the index.
REVERSE   Required keyword for reverse indexes.

Determining Which Type of Index to Use

Oracle provides a wide range of index types and features. The correct use of indexes results in well performing and scalable database application. Conversely, if you incorrectly or unwisely implement a feature, there may be detrimental performance implications. The table below summarizes the various Oracle index types available. At first glance, this is a long list and may be somewhat overwhelming to somebody new to Oracle. Deciding which index type to use is not as daunting as it might initially seem. For most applications, you should simply use the default B-tree index type.
Note Several of the index types listed in the table below are actually just variations on the basic, B-tree index. A reverse-key index, for example, is merely a B-tree index optimized for evenly spreading I/O when the index value is sequentially generated and inserted with similar values.

Table 5-7 Part 1: Table of Oracle Indexes

Table 5-7 Part 2: Table of Oracle Indexes