How Do I Use Exception Handling in PL/SQL

 Introduction

Exception handling in PL/SQL is a crucial technique that helps you manage errors and unexpected situations gracefully in your Oracle APEX applications. By using exception handling, you can catch runtime errors, prevent application crashes, and provide meaningful messages or corrective actions when problems occur. Learning how to implement proper exception handling improves the reliability and user experience of your applications.

In Oracle APEX, exception handling in PL/SQL lets you manage errors that occur during code execution. By capturing exceptions, you can prevent your application from crashing and provide meaningful feedback or corrective actions. PL/SQL uses the EXCEPTION block within a PL/SQL block to handle errors effectively.

Step 1: Structure of Exception Handling
A PL/SQL block with exception handling has three sections: DECLARE (optional), BEGIN, and EXCEPTION.

DECLARE
  -- variable declarations
BEGIN
  -- executable statements
EXCEPTION
  -- error handling statements
END;

Step 2: Using Built-in Exceptions
PL/SQL has many predefined exceptions like NO_DATA_FOUND, TOO_MANY_ROWS, ZERO_DIVIDE, etc. You can handle these as follows:

BEGIN
  SELECT first_name INTO v_name FROM employees WHERE employee_id = 9999;
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    APEX_DEBUG.MESSAGE('No employee found with this ID.');
END;

Step 3: Handling Multiple Exceptions
You can handle multiple exceptions in one block by listing them individually.

BEGIN
  -- code that may raise exceptions
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    APEX_DEBUG.MESSAGE('No data found.');
  WHEN ZERO_DIVIDE THEN
    APEX_DEBUG.MESSAGE('Division by zero error.');
  WHEN OTHERS THEN
    APEX_DEBUG.MESSAGE('Unexpected error occurred.');
END;

Step 4: Using WHEN OTHERS Clause
WHEN OTHERS catches any exceptions not explicitly handled earlier. It’s good practice to include it to avoid unhandled errors.

Step 5: Raising Custom Exceptions
You can define and raise your own exceptions to handle specific business rules.

DECLARE
  e_invalid_value EXCEPTION;
BEGIN
  IF :P1_AGE < 0 THEN
    RAISE e_invalid_value;
  END IF;
EXCEPTION
  WHEN e_invalid_value THEN
    APEX_DEBUG.MESSAGE('Age cannot be negative.');
END;

Step 6: Best Practices

• Always handle exceptions to maintain application stability.

• Use meaningful messages to inform users or developers.

• Avoid empty exception blocks that suppress errors silently.

• Log errors for troubleshooting when necessary.

• Use APEX_DEBUG.MESSAGE during development to trace issues.

Exception handling in PL/SQL is vital for building reliable Oracle APEX applications. It helps you control error situations, maintain data integrity, and improve user experience by handling problems gracefully.

Conclusion

Mastering exception handling in PL/SQL allows you to build robust and fault-tolerant Oracle APEX applications. It ensures that errors are caught and handled appropriately, helping maintain data integrity and smooth application flow. Proper use of exception handling not only improves debugging and maintenance but also enhances the overall stability and professionalism of your software solutions.

Additional Example

Errors can occur in PL/SQL, and handling them properly prevents application crashes.

BEGIN

    UPDATE EMPLOYEES SET SALARY = SALARY + 1000 WHERE EMPLOYEE_ID = :P1_EMP_ID;

EXCEPTION

    WHEN NO_DATA_FOUND THEN

        :P1_MESSAGE := 'No employee found with this ID.';

    WHEN OTHERS THEN

        :P1_MESSAGE := 'An unexpected error occurred.';

END;

This ensures that meaningful error messages are displayed instead of generic system errors.