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Snippet Name: INDEXES: Bitmap Join Indexes

Description: In a Bitmap Index, each distinct value for the specified column is associated with a bitmap where each bit represents a row in the table. A '1' means that row contains that value, a '0' means it doesn't.

Bitmap Join Indexes extend this concept such that the index contains the data to support the join query, allowing the query to retrieve the data from the index rather than referencing the join tables. Since the information is compressed into a bitmap, the size of the resulting structure is significantly smaller than the corresponding materialized view.

A bitmap join index is defined on a single table. For an index key made up of dimension table columns, it stores the fact table rowids corresponding to that key.

Restrictions on Bitmap Join Indexes

In addition to the restrictions on bitmap indexes in general (see BITMAP), the following restrictions apply to bitmap join indexes:

- You cannot create a bitmap join index on an index-organized table or a temporary table.

- No table may appear twice in the FROM clause.
- You cannot create a function-based join index.

- The dimension table columns must be either primary key columns or have unique constraints.

- If a dimension table has a composite primary key, each column in the primary key must be part of the join.

- You cannot specify the local_index_clauses unless the fact table is partitioned.

Also see:
» INDEXES: View table indexes
» INDEXES: Analyze Index
» INDEXES: Block Dump
» INDEXES: Rebuild Reverse
» INDEXES: ENABLE (function-based index)
» INDEXES: DISABLE (function-based index)
» INDEXES: Alter Index Parallel
» INDEXES: Alter Index Deallocate Unused
» INDEXES: Alter Index Allocate Extent
» INDEXES: Virtual / NoSegment
» INDEXES: Reverse Key Indexes
» INDEXES: Bitmap Indexes
» INDEXES: Unique indexes
» INDEXES: Parallel Index
» INDEXES: Compute Statistics
» INDEXES: Function-Based Index
» INDEXES: Alter index
» INDEXES: Single Column Non-unique
» INDEXES: Index Usage Notes
» Compressed Indexes
» Create INDEX

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Language: PL/SQL
Highlight Mode: PLSQL
Last Modified: March 10th, 2009

ON <table_name> (<table_name.column_name>)
FROM <table_name, table_name>
WHERE <join_condition> 
-- for example:
ON    sales(customers.state)
FROM  sales, customers
WHERE sales.cust_id = customers.cust_id;

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