Explain the Oracle exception handling mechanism

Introduction to Oracle Exception Handling

Oracle Exception Handling is a powerful feature in Oracle Database Management System that allows developers to manage runtime errors or exceptions effectively. An exception is an error condition during a program execution. Oracle supports numerous predefined exceptions and also allows the programmer to define their own exceptions. Exception handling ensures that the flow of the program does not break when an exception occurs. For example, if a program has a division by zero error, the program will terminate abruptly during runtime. However, with exception handling, the error can be caught and a meaningful message can be displayed, thereby avoiding program termination.

Types of Exceptions in Oracle

Oracle exceptions can be broadly classified into three types:

1. Predefined Exceptions: These are exceptions that are implicitly raised by Oracle server and are known to Oracle in advance. For example, ZERO_DIVIDE is raised if a program attempts to divide a number by zero.

2. Non-Predefined Exceptions: These are exceptions that are not implicitly raised by Oracle server and are not known to Oracle in advance. They are raised due to the conditions that are specific to the Oracle server environment.

3. User-Defined Exceptions: These are exceptions that are explicitly defined by the programmer in the declaration section of the program. They are raised explicitly by the RAISE statement within the program.

Exception Handling Mechanism in Oracle

Oracle uses a set of keywords to handle exceptions. These are BEGIN, EXCEPTION, WHEN, THEN, and END. The general syntax for exception handling in Oracle is as follows:

BEGIN
   -- executable statements
EXCEPTION
   WHEN exception1 THEN
      -- exception handler
   WHEN exception2 THEN
      -- exception handler
   ...
END;

In the above syntax, the program execution starts at the BEGIN keyword and ends at the END keyword. If an exception occurs in the executable statements, control is passed to the EXCEPTION keyword and then to the appropriate exception handler.

How to Raise Exceptions in Oracle

In Oracle, exceptions can be raised using the RAISE statement or the RAISE_APPLICATION_ERROR procedure. The RAISE statement is used to explicitly raise a predefined exception or a user-defined exception. The syntax for the RAISE statement is as follows:

RAISE exception_name;

The RAISE_APPLICATION_ERROR procedure is used to issue a user-defined error messages from stored subprograms. The syntax for the RAISE_APPLICATION_ERROR procedure is as follows:

RAISE_APPLICATION_ERROR (error_number, message[, {TRUE | FALSE}]);

How to Handle Exceptions in Oracle

In Oracle, exceptions can be handled using the WHEN OTHERS THEN statement, and the SQLCODE and SQLERRM functions. The WHEN OTHERS THEN statement is used to handle all exceptions that are not explicitly handled by a named exception handler.

The SQLCODE function returns the numeric code of the exception being handled. The SQLERRM function returns the message associated with the exception being handled. The syntax for these functions is as follows:

SQLCODE;
SQLERRM;

Conclusion

In conclusion, Oracle exception handling is a powerful feature that allows developers to manage runtime errors effectively. Understanding and properly implementing exception handling in Oracle databases is crucial for building robust and error-free applications.

Summary

Oracle Exception Handling is a powerful feature in Oracle Database Management System that allows developers to manage runtime errors or exceptions effectively. It includes predefined exceptions, non-predefined exceptions, and user-defined exceptions. The exception handling mechanism in Oracle uses keywords like BEGIN, EXCEPTION, WHEN, THEN, and END. Exceptions can be raised using the RAISE statement or the RAISE_APPLICATION_ERROR procedure. Exceptions can be handled using the WHEN OTHERS THEN statement, and the SQLCODE and SQLERRM functions.

Analogy

Exception handling in Oracle is like having a safety net while performing acrobatics. If something goes wrong, instead of falling to the ground, the safety net catches you and allows you to continue your performance without any interruption.