How to Alter Index in Oracle Examples
In Oracle Database, indexes play a crucial role in optimizing query performance by providing faster data retrieval. However, there may be situations where you need to alter an existing index to accommodate changes in your database schema or to improve performance. This article provides examples of how to alter indexes in Oracle Database using SQL commands.
1. Adding Columns to an Existing Index
One common scenario is adding a column to an existing index. This can be done using the following SQL command:
“`sql
ALTER INDEX index_name ADD (column_name);
“`
For example, if you have an index named “idx_employee_department” on the “employees” table and you want to add the “salary” column to the index, you can use the following command:
“`sql
ALTER INDEX idx_employee_department ADD (salary);
“`
2. Dropping Columns from an Existing Index
Similarly, you can drop a column from an existing index using the following SQL command:
“`sql
ALTER INDEX index_name DROP (column_name);
“`
For instance, if you want to remove the “salary” column from the “idx_employee_department” index, you can use the following command:
“`sql
ALTER INDEX idx_employee_department DROP (salary);
“`
3. Rebuilding an Index
Rebuilding an index can help improve performance if the index has become fragmented. To rebuild an index, use the following SQL command:
“`sql
ALTER INDEX index_name REBUILD;
“`
For example, to rebuild the “idx_employee_department” index, you can use the following command:
“`sql
ALTER INDEX idx_employee_department REBUILD;
“`
4. Changing Index Storage Parameters
You can also change the storage parameters of an existing index using the following SQL command:
“`sql
ALTER INDEX index_name STORAGE (initial_size, next_size, max_size);
“`
For instance, if you want to modify the storage parameters of the “idx_employee_department” index to have an initial size of 100MB, a next size of 10MB, and a maximum size of 1GB, you can use the following command:
“`sql
ALTER INDEX idx_employee_department STORAGE (100M, 10M, 1G);
“`
5. Changing Index Organized Table (IOT) Storage Parameters
If you are working with an Index Organized Table (IOT), you can change the storage parameters using the following SQL command:
“`sql
ALTER INDEX index_name ORGANIZATION IOT (table_name) STORAGE (initial_size, next_size, max_size);
“`
For example, to modify the storage parameters of an IOT named “iot_employee_department” with an initial size of 100MB, a next size of 10MB, and a maximum size of 1GB, you can use the following command:
“`sql
ALTER INDEX idx_employee_department ORGANIZATION IOT (iot_employee_department) STORAGE (100M, 10M, 1G);
“`
By following these examples, you can effectively alter indexes in Oracle Database to meet your requirements and optimize performance.
