What are the Oracle index types?

Oracle index types include: 1. B-Tree index; 2. Bitmap index; 3. Function index; 4. Hash index; 5. Reverse key index; 6. Local index; 7. Global Index; 8. Domain index; 9. Bitmap connection index; 10. Composite index. Detailed introduction: 1. B-Tree index is a self-balancing tree data structure that can efficiently support concurrent operations. In Oracle database, B-Tree index is the most commonly used index type; 2. Bit Graph index is an index type based on bitmap algorithm and so on.

Oracle database supports multiple index types. The following are some of the common types:

1. B-Tree index: B-Tree (Balanced Tree) is a self-balancing tree data structure that can efficiently support concurrent operations. In Oracle database, B-Tree index is the most commonly used index type. B-Tree index organizes data in a tree structure, with faster query speed and lower maintenance cost.

2. Bitmap Index: Bitmap Index is an index type based on bitmap algorithm. It creates a bitmap for each unique value in the indexed column and then uses the bitmap to retrieve and sort the data. Bitmap indexes are more suitable for columns with many repeated values ​​and can provide fast uniqueness checks and range queries.

3. Function Index: Function Index is a type of index calculated based on functions or expressions. Functional indexes can apply functions or expressions on index columns to provide more flexible query capabilities. For example, you can use functional indexes to speed up string conversion or date calculation operations on specific columns.

4. Hash Index: Hash Index is an index type based on hash algorithm. It maps the index column values ​​into a hash table based on a hash function and then uses the hash value to retrieve the data. Hash indexes are suitable for exact queries and equality queries, but may be less efficient when handling range queries and sort operations.

5. Reverse key index: Reverse key index (Reverse Key Index) is an index type that reverses the value of the index column. It is suitable for string type columns and can improve the efficiency of certain query operations. A reverse key index creates a new index column, reverses the character order of the original data, and then builds a B-Tree index.

6. Local Index: Local Index (Local Index) is an index type for partitioned tables. A local index only creates a separate B-Tree index for each partition, rather than creating a global index on the entire table. This reduces index maintenance costs and storage space requirements while improving query performance.

7. Global Index: Global Index is a type of index created on the entire table. Global indexes are suitable for efficient query operations on the entire table. A global index requires more storage space and maintenance costs than a local index, but it provides more comprehensive query coverage.

8. Domain Index: Domain Index (Domain Index) is an index type based on column value range division. It maps data into different B-Tree indexes based on the range of column values, providing more precise query matching. Domain indexes are suitable for columns with obvious range restrictions, such as dates, currencies, etc.

9. Bitmap Connect Index: Bitmap Connect Index is an index type used for connection operations. It speeds up join operations by creating bitmap indexes on the join columns. Bitmap join indexes can provide fast join matching and sorting operations, and are especially suitable for scenarios where large tables and complex join operations are processed.

10. Composite Index: Composite Index (Composite Index) is an index type based on multiple columns. A composite index can contain one or more columns, and the index is built by combining values ​​from multiple columns. Composite indexes are suitable for optimization of multi-column queries and join operations. In a composite index, the order of the columns is important because the query optimizer will optimize based on the leftmost column.

These are some common index types in Oracle database, each type has its specific applicable scenarios, advantages and disadvantages. In actual applications, the choice of which type of index depends on the comprehensive consideration of factors such as table structure, data distribution, query requirements, and performance requirements.

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