In SQL, a partitioned index is defined within a partitioned table, and the CREATE INDEX statement can be used with the PARTITION clause to create such an index. The usage might vary slightly depending on which database system you are using, as the SQL syntax and features can differ (e.g., PostgreSQL, Oracle, SQL Server, etc.). Below is a general overview of how to create a partitioned index using the CREATE INDEX statement with the PARTITION clause. The example is particularly applicable to systems like Oracle, which supports partitioning schemas.
General Syntax
Here's a general syntax for creating a partitioned index:
CREATE INDEX index_name
ON table_name (column1, column2, ...)
[LOCAL | GLOBAL]
[PARTITION partition_name]
Parameters:
- index_name: The name of the index you want to create.
- table_name: The name of the table on which you're creating the index.
- (column1, column2, ...): The columns of the table you wish to index.
- LOCAL | GLOBAL:
- LOCAL: Create the index on each partition of the table.
- GLOBAL: Create a single index that spans all partitions.
- PARTITION partition_name: Specific partition that the index applies to.
Example of Creating a Partitioned Index
Assuming you have a partitioned table sales_data with partitions based on year, here’s how you might create a local partitioned index:
CREATE INDEX idx_sales_date
ON sales_data (sales_date)
LOCAL
PARTITION p_2020; -- Specific partition
In this example:
- idx_sales_date is the name of the index.
- The index is applied to the sales_date column of the sales_data table.
- The LOCAL clause specifies that the index is to be created for each partition of the table.
- The PARTITION p_2020 clause indicates that this index applies specifically to the p_2020 partition.
Creating a Global Index
If you want to create a global index that covers all partitions:
CREATE INDEX idx_sales_global
ON sales_data(sales_date)
GLOBAL; -- A single global index
Important Considerations
- Make sure that the columns you are indexing can effectively reduce the search time (i.e., they should be frequently queried).
- The decision to create a LOCAL or GLOBAL index can affect performance, particularly with insert, update, and delete operations.
- Always refer to your database documentation, as the syntax and capabilities might vary for different RDBMS.
Conclusion
Using the CREATE INDEX statement with the PARTITION clause allows you to optimize query performance on partitioned tables by organizing index data to align with the logical partitioning of the table.