A cursor for loop in PL/SQL streamlines iteration over result sets by automatically declaring a record and looping through each row returned by a query. This construct reduces boilerplate code and helps developers write cleaner, more maintainable database logic.
By combining implicit cursor handling with a fixed loop structure, the cursor for loop handles opening, fetching, and closing automatically, which minimizes common errors and improves readability.
| Term | Description | Syntax Element | Related Concepts |
|---|---|---|---|
| Cursor For Loop | PL/SQL loop that iterates over rows returned by a query | FOR record_name IN cursor_name LOOP | Implicit Cursors |
| Implicit Cursor | Automatically managed by Oracle during SQL execution | SQL%ROWCOUNT, SQL%FOUND | Cursor For Loop |
| Record | Variable representing a row fetched from the cursor | record_name.column_name | Cursor For Loop |
| Open-Read-Close Cycle | Automated within the loop, reducing manual steps | FOR ... LOOP ... END LOOP | Explicit Cursors |
Cursor For Loop Basics and Syntax
Essential Structure
The fundamental syntax of a cursor for loop starts with the FOR keyword, followed by a loop variable, the IN keyword, and a query string enclosed in parentheses. The loop body then references the loop variable to process columns from the current row. Oracle implicitly declares a record, opens an implicit cursor, fetches rows, and exits when no more rows are available.
This structure removes the need to declare a cursor manually, call OPEN, FETCH, and CLOSE statements, and handle the loop index. Developers gain a concise way to iterate over query results while relying on PL/SQL to manage cursor lifecycle and exception handling within the loop.
Under the hood, the database still performs OPEN, FETCH, and CLOSE operations, but the engine encapsulates these steps safely. The loop terminates automatically when the cursor exhausts the result set, making the construct robust and less error-prone than manually written cursor loops.
Performance and Resource Management
Cursor for loops leverage bulk operations behind the scenes and can be efficient for typical row-by-row processing. However, for very large data sets, developers may still consider BULK COLLECT and FORALL to minimize context switches between SQL and PL/SQL engines. Understanding when to use a simple cursor for loop versus bulk processing helps balance clarity and performance.
Resource usage remains predictable because the loop releases rows and internal cursor structures promptly upon completion. This predictable cleanup behavior supports stable transaction management and reduces the risk of resource leaks when coding batch jobs or reporting logic.
Declaring Variables Inside the Loop
Accessing Columns
Inside the loop body, you reference column values through the loop record using dot notation, such as record_name.column_name. This approach keeps code readable and avoids the need to declare additional variables for each column unless specific calculations or transformations are required.
The record fields automatically match the selected columns in the query, including their data types. As a result, you can directly use column values in DML statements, condition checks, or output routines without manual type mapping.
Custom Record Types
For more advanced scenarios, you can define your own record type in the declaration section and use it with a cursor for loop by qualifying the loop with that record type. This technique provides flexibility when the query structure does not directly map to a table or when combining columns from multiple sources.
Using a tailored record type can improve self-documentation and enable consistent handling of complex business rules across procedures and functions. However, most standard queries work effectively with the default implicit record provided by the cursor for loop.
Error Handling and Transaction Control
Managing Exceptions
PL/SQL processes exceptions inside cursor for loops in a straightforward manner. When an error occurs during fetching or processing, the loop stops, and control transfers to the enclosing block’s exception section. You can log the problematic row, perform cleanup, and, when appropriate, continue processing remaining rows using SAVEPOINTS or conditional handling.
Because the loop manages cursor closure automatically, you do not need explicit CLOSE statements in the normal flow. However, it is still good practice to ensure that any autonomous transaction or external resource usage is committed or rolled back deliberately according to business rules.
Transaction Boundaries
Cursor for loops do not implicitly commit or roll back unless you explicitly issue COMMIT or ROLLBACK statements. This design keeps data manipulation predictable and allows you to group multiple operations within a single transaction for better consistency.
For long-running batch processes, consider strategic commit intervals to avoid excessive undo retention and table locking. Balancing transaction scope with loop granularity helps maintain performance while preserving data integrity during complex operations.
Best Practices and Recommendations
- Use cursor for loops for straightforward row-by-row processing where code clarity is essential.
- Consider BULK COLLECT and FORALL for large data sets to reduce context switches and improve performance.
- Keep transaction boundaries explicit by placing COMMIT or ROLLBACK at logical batch points outside the loop when appropriate.
- Use FOR UPDATE only when you need to modify rows later in the loop, and always qualify updates with WHERE CURRENT OF.
- Test edge cases, such as empty result sets and null values, to ensure stable behavior in production.
FAQ
Reader questions
Can I use a cursor for loop with dynamic SQL in PL/SQL?
Yes, you can use a cursor for loop with dynamic SQL by opening a native dynamic cursor via the OPEN FOR syntax and then looping over it. This approach lets you parameterize queries at runtime while still benefiting from automatic cursor management.
Does a cursor for loop lock rows during iteration?
By default, a cursor for loop does not lock rows unless you explicitly use the FOR UPDATE clause. Adding FOR UPDATE opens the cursor in update mode and allows you to modify the fetched rows later within the loop using the WHERE CURRENT OF syntax.
How does a cursor for loop compare to a while loop in PL/SQL?
A cursor for loop is more concise and less error-prone than a while loop when working with query results because it handles cursor opening, fetching, and closing automatically. A while loop gives you finer control but requires manual management of cursor states and exit conditions.
What happens if the query returns no rows in a cursor for loop?
If the query returns no rows, the cursor for loop body simply does not execute, and control moves immediately to the next statement after the loop. No runtime errors occur, making this behavior safe for conditional processing.