Handling errors and exceptions while working with SQL cursors

19 Sep 2023

Working with SQL cursors is a common practice in database programming. Cursors allow you to retrieve and manipulate data row by row, providing more control over result sets. However, it is important to handle errors and exceptions that may occur while using cursors to ensure the integrity and reliability of your database operations.

In this blog post, we will explore best practices for handling errors and exceptions when working with SQL cursors.

1. Understanding SQL Cursor Errors

SQL cursors can generate various errors and exceptions during their lifecycle. Some common errors include:

CURSOR_ALREADY_OPEN: This error occurs when you try to open a cursor that is already open.
CURSOR_NOT_OPEN: This error occurs when you try to perform operations on a cursor that is not open.
NO_DATA_FOUND: This error is raised when a cursor fetch operation does not return any rows.
INVALID_CURSOR: This error occurs when attempting to fetch from a cursor that is no longer valid.
CURSOR_ALREADY_EXISTS: This error is raised when you try to create a cursor that already exists.

2. Implementing Error Handling

To handle errors and exceptions in SQL cursors, you can use a combination of error checking and exception handling techniques.

Here is an example of how you can handle errors and exceptions while working with cursors:

DECLARE
  CURSOR c_employee IS
    SELECT * FROM employees;

  v_employee employees%ROWTYPE;
BEGIN
  OPEN c_employee;

  LOOP
    FETCH c_employee INTO v_employee;
    EXIT WHEN c_employee%NOTFOUND;

    -- Perform operations on the fetched row

    -- error checking
    IF SQL%ISOPEN THEN
      -- cursor is open
      -- perform error handling for specific errors
      -- example: handle CURSOR_ALREADY_OPEN error
      IF SQL%FOUND AND SQLERRM = 'CURSOR_ALREADY_OPEN' THEN
        -- handle the error
      ELSE
        -- other error handling logic
      END IF;
    ELSE
      -- cursor is closed
      -- handle closed cursor error (CURSOR_NOT_OPEN)
    END IF;

  END LOOP;

  CLOSE c_employee;
EXCEPTION
  WHEN OTHERS THEN
    -- general exception handling logic
END;

In the example above, we first declare a cursor named c_employee. We then open the cursor using the OPEN statement and iterate through the result set using a loop. Inside the loop, we perform operations on each fetched row.

The error handling logic includes checking if the cursor is open using SQL%ISOPEN, and handling specific errors using conditional statements. General exception handling for any other unhandled errors is also included using the WHEN OTHERS clause.

Conclusion

Handling errors and exceptions when working with SQL cursors is crucial to ensure the smooth execution of database operations. By implementing error checking and exception handling techniques, you can enhance the reliability and integrity of your code.

Remember to thoroughly understand the possible errors and exceptions that can occur with cursors, and tailor your error handling strategy accordingly. Applying these best practices will help you build robust and error-resistant database applications.

#SQLCursors #ErrorHandling