Oracle index is a special data structure that accelerates data access and improves query performance by storing pointers to data in tables. Oracle provides a variety of index types, including B-Tree index, bitmap index, function index, and hash index. Indexes are especially suitable for data queries that require frequent filtering of specific columns or accessing large tables, but creating and maintaining indexes requires additional space and overhead, and large amounts of indexes may also reduce query efficiency.
What is Oracle Indexing
Indexing plays a crucial role in Oracle databases, helping to speed up access to data and thus improve query performance.
How index works
An index is a special data structure in a database that is created based on the column values ??of a table. The index stores pointers to the actual data in the table, which are sorted by column values. When querying a table, Oracle uses an index to find specific values, thus avoiding scanning the entire table.
Type of index
Oracle provides multiple types of indexes to meet different performance needs:
- B-Tree Index : This is the most common index type, which uses a balanced tree structure to store data.
- Bitmap index : suitable for columns with a large number of duplicate values.
- Function index : Created based on expressions on column values.
- Hash index : stores data based on a hash algorithm, suitable for equivalent comparison queries.
Create an index
You can create an index in Oracle with the following command:
<code>CREATE INDEX index_name ON table_name (column_name);</code>
When to use index
Indexing is useful for:
- Queries are often filtered based on specific columns.
- The table is very large, and scanning the entire table will take a lot of time.
- The query needs to return a large number of rows.
Index limitations
While indexing can improve query performance, there are some limitations:
- Creating and maintaining indexes requires additional space and overhead.
- Insert, update, and delete operations may cause index invalidation, which affects query performance.
- Too many indexes may lead to reduced query efficiency.
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