What is the indexing mechanism in oracle

The index in Oracle is a data structure used to quickly find data. It creates a copy of the table column value and avoids a full table scan. Supports B-Tree, Bitmap, Hash, reverse key, XML and other index types, created through the CREATE INDEX command; Oracle automatically maintains the index; using indexes can reduce query time, improve performance, support more complex and faster queries, and simplify data Maintenance; however, it should be noted that indexes occupy storage space, maintaining indexes incurs additional overhead, and not all queries can benefit from indexes.

Index mechanism in Oracle

The index in Oracle is a data structure that can quickly search the database data in the table. Indexes work by creating a copy of the column values ​​in the table, thereby avoiding a full table scan of the table.

Index Type

Oracle supports multiple index types, each type has its specific purpose:

• B- Tree index: Suitable for quickly finding a single value or a range of values.
• Bitmap index: Suitable for performing fast bit operations on large amounts of data.
• Hash index: Suitable for quickly finding a single value based on its hash value.
• Reverse key index: Used to find data in multiple column order.
• XML Index: Allows fast queries to be performed on XML data.

Index creation

You can create an index by running the following command:

<code>CREATE INDEX <索引名称> ON <表名称> (<列名称>)</code>

For example, to create an index named customers To create a B-Tree index on the name column on the table, you can use the following command:

<code>CREATE INDEX idx_customers_name ON customers (name)</code>

Index maintenance

Oracle will automatically maintain the index. When data is inserted, updated, or deleted from the table, the index is updated accordingly.

Index Benefits

Using indexes has the following benefits:

• Reduce query time
• Improve performance
• Support more complex and faster queries
• Simplify data maintenance

Index considerations

When using indexes, you need to pay attention The following points:

• Indexes will take up storage space.
• Maintaining indexes will incur additional overhead.
• Not all queries can benefit from indexes.

The above is the detailed content of What is the indexing mechanism in oracle. For more information, please follow other related articles on the PHP Chinese website!