A database cursor is a control structure that enables traversal over records in a database. Think of it as a pointer that can move through the rows of a query result set, allowing you to process data one row at a time rather than as a complete set.
A cursor is a fundamental database concept that acts as a control structure for navigating through query results. Unlike regular SQL queries that return entire result sets at once, a cursor allows you to process records one by one, providing precise control over data retrieval and manipulation.
Using a cursor involves six key steps. First, DECLARE the cursor by associating it with a SELECT statement. Then OPEN the cursor to execute the query and populate the result set. Next, FETCH rows one by one in a loop. PROCESS each retrieved row as needed. Finally, CLOSE the cursor to deactivate it and DEALLOCATE to destroy it completely.
Here's a practical SQL cursor example. We declare a cursor for employees in the IT department, open it to execute the query, then fetch rows in a loop. The FETCH_STATUS variable tells us when we've reached the end. After processing each row, we fetch the next one. Finally, we close and deallocate the cursor to free resources.
Cursors are best used when you need row-by-row processing, complex business logic per record, or memory constraints with large result sets. They're also useful for integration with external systems. However, avoid cursors for simple operations due to performance overhead. Set-based operations are generally faster and more efficient for bulk data manipulation.
To summarize, cursors are powerful database tools that provide row-by-row access to query results. Always remember to close and deallocate cursors, choose appropriate cursor types, and minimize their scope. While they offer precise control and flexibility, use them judiciously due to performance implications. They excel in scenarios requiring complex per-row logic or integration with external systems.
Here's a practical SQL cursor example. We declare a cursor for employees in the IT department, open it to execute the query, then fetch rows in a loop. The FETCH_STATUS variable tells us when we've reached the end. After processing each row, we fetch the next one. Finally, we close and deallocate the cursor to free resources.
Cursors are best used when you need row-by-row processing, complex business logic per record, or memory constraints with large result sets. They're also useful for integration with external systems. However, avoid cursors for simple operations due to performance overhead. Set-based operations are generally faster and more efficient for bulk data manipulation.
To summarize, cursors are powerful database tools that provide row-by-row access to query results. Always remember to close and deallocate cursors, choose appropriate cursor types, and minimize their scope. While they offer precise control and flexibility, use them judiciously due to performance implications. They excel in scenarios requiring complex per-row logic or integration with external systems.