Exceptional Handling in PLSQL

In PL/SQL (Procedural Language/Structured Query Language), Oracle provides a robust exception handling mechanism to deal with errors and unexpected conditions during the execution of programs. Exception handling allows developers to handle runtime errors, ensuring that the application does not crash abruptly and allowing developers to take corrective actions or display user-friendly error messages.

What is an Exception?

An exception is an error condition or unexpected event that occurs during the execution of a PL/SQL block. There are two types of exceptions:

1. Predefined Exceptions: These are exceptions automatically raised by Oracle when standard errors occur (like NO_DATA_FOUND, ZERO_DIVIDE, TOO_MANY_ROWS, etc.).

2. User-defined Exceptions: These are exceptions that the developer can define and raise explicitly using the RAISE keyword.

Exception Handling Structure in PL/SQL

The EXCEPTION keyword is used to define an exception-handling section in a PL/SQL block. It is part of a PL/SQL block's structure, which typically follows this order:

1. Declaration Section: Variables, cursors, and user-defined exceptions are declared here.

2. Execution Section: Contains the executable code where actual SQL statements or PL/SQL logic are implemented.

3. Exception Section: This is where errors are caught and handled.

Syntax

DECLARE
   -- Declaration section
   -- Variables, cursors, user-defined exceptions are declared here.

BEGIN
   -- Execution section
   -- Contains the code which might raise an exception.

EXCEPTION
   -- Exception section
   WHEN exception_name1 THEN
      -- Code to handle the exception
   WHEN exception_name2 THEN
      -- Code to handle another exception
   WHEN OTHERS THEN
      -- Handles all other exceptions not explicitly named
END;

Conclusion

The PL/SQL exception handling mechanism is a powerful tool that allows developers to handle both predefined and user-defined exceptions effectively. By using the EXCEPTION block along with mechanisms like RAISE, RAISE_APPLICATION_ERROR, and PRAGMA EXCEPTION_INIT, developers can catch and handle errors, ensuring that programs run smoothly and handle errors gracefully. This improves the robustness of applications and ensures that even in the event of errors, the application can provide meaningful feedback to users or take corrective actions.