What is an Index?

What is an Index?

- Index in oracle helps to trace the information faster just like an index in a book.

- Index entries keep information about the columns that are part of the index in a sorted order.

- If you query data with an index, the data retrieval is much faster.

Use the CREATE INDEX statement to create an index on:

a. One or more columns of a table, a partitioned table, an index-organized table, or a cluster.
b. One or more scalar typed object attributes of a table or a cluster.
c. A nested table storage table for indexing a nested table column.

- An index is a schema object that contains an entry for each value that appears in the indexed column(s) of the table or cluster and provides direct, fast access to rows.

Oracle Database supports several types of index:

1. Normal indexes. (By default, Oracle Database creates B-tree indexes.)

2. Bitmap indexes, which store rowids associated with a key value as a bitmap.

3. Partitioned indexes, which consist of partitions containing an entry for each value that appears in the indexed column(s) of the table.

4. Function-based indexes, which are based on expressions. They enable you to construct queries that evaluate the value returned by an expression, which in turn may include built-in or user-defined functions.

5. Domain indexes, which are instances of an application-specific index of type indextype.
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