Raise application error in PL/SQL

PL/SQL is an extension of SQL, with procedural capabilities enabling developers to make use of SQL for developing complex, reusable, and well-structured code toward database managemen

t. Exception handling may be one of the most crucial aspects when it comes to creating robust PL/SQL code in order to catch errors, process them, and manage them graciously. Among the two important components are RAISE and RAISE_APPLICATION_ERROR built-in procedures through which effective error management can be done with PL/SQL. In this article we will cover PL/SQL Exception Handling by thoroughly RAISE and RAISE_APPLICATION_ERROR. RAISE_APPLICATION_ERROR Syntax , Oracle PL/SQL Error Management, User-Defined Exceptions in PL/SQL, use, and best practice for creation of custom error messages on PL/SQL will be analysed with the help of examples and tables.

Introduction to PL/SQL Exception Handling

PL/SQL exception handling is how we handle errors which may come up in the course of program execution. When a problem occurs, PL/SQL transfers control to the EXCEPTION block where we can specify how the program should behave on a problem that has arisen. This is important to avoid applications crashing at unexpected times and recovering from problems in an amicable manner.

Exceptions in PL/SQL are categorised into two types:

• Built-in Exceptions: Oracle raises them automatically with standard errors, including NO_DATA_FOUND, ZERO_DIVIDE.
• User-Defined Exceptions: In this case, an explicit exception is raised by a programmer using the RAISE or RAISE_APPLICATION_ERROR statement to indicate specific error conditions in their code.

What is the RAISE Statement?

The RAISE statement in PL/SQL explicitly raises an exception. This has to be either a predefined one or one defined by the user. It allows the developer to flag specific conditions that require special handling when the code is executed.

Syntax of RAISE in PL/SQL

RAISE exception_name;

Example of RAISE in PL/SQL

Consider a scenario where we need to raise a custom exception if the value of an employee’s salary is too low:

DECLARE
  low_salary EXCEPTION;
  v_salary NUMBER := 2000;
BEGIN
  IF v_salary < 3000 THEN
    RAISE low_salary;  -- Raising the user-defined exception
  END IF;
EXCEPTION
  WHEN low_salary THEN
    DBMS_OUTPUT.PUT_LINE('Error: Salary is below the acceptable limit.');
END;

In this Example:

• We make a user-defined exception low_salary.
• The exception gets raised if the salary of the employee is less than 3000.
• The EXCEPTION block catches this exception and deals with it.

User-Defined Exceptions in PL/SQL

User-defined exceptions in PL/SQL provide a powerful mechanism for handling specific error conditions that are not covered by the standard exceptions. By declaring your own exceptions, you can create more meaningful and context-specific error messages that enhance the robustness of your applications. To define a user-defined exception, you simply declare it in the declarative section of your PL/SQL block using the syntax exception_name EXCEPTION;. You can then raise this exception using the RAISE statement when a particular condition is met, allowing for precise control over error handling. This capability not only improves code readability but also aids in debugging by providing clearer insights into the nature of errors encountered during execution. Overall, user-defined exceptions empower developers to tailor their error management strategies to fit the unique requirements of their applications

User defined exceptions help developers to define specific business logic that predefined ones may not. You declare an exception in the DECLARE section, and then you can explicitly raise it by using the RAISE statement based on a given condition.

Declaring and Raising a User-Defined Exception

• Declare: The user-defined exception is declared in the DECLARE section.
• Raise: The exception is raised in the BEGIN section based on a particular condition.
• Handle: It is handled in the EXCEPTION block.

DECLARE
  insufficient_funds EXCEPTION;
  account_balance NUMBER := 500;
  withdrawal_amount NUMBER := 1000;
BEGIN
  IF withdrawal_amount > account_balance THEN
    RAISE insufficient_funds;
  END IF;
  
  DBMS_OUTPUT.PUT_LINE('Withdrawal processed successfully.');
  
EXCEPTION
  WHEN insufficient_funds THEN
    DBMS_OUTPUT.PUT_LINE('Error: Insufficient funds in the account.');
END;

What is RAISE_APPLICATION_ERROR in PL/SQL?

RAISE_APPLICATION_ERROR is a built-in procedure in Oracle PL/SQL that allows developers to generate custom error messages and error codes. It provides a more flexible way to raise user-defined exceptions and communicate specific problems to the application or user.

Syntax of RAISE_APPLICATION_ERROR

RAISE_APPLICATION_ERROR(error_number, message[, keep_errors]);

Where:

• error_number: A negative number in the range of -20000 to -20999. This is the custom error code.
• message: A descriptive message explaining the error.
• keep_errors (optional): A Boolean value that, if set to TRUE, preserves the original error message along with the custom one.

Example of RAISE_APPLICATION_ERROR

DECLARE
  v_balance NUMBER := 500;
  v_withdrawal NUMBER := 1000;
BEGIN
  IF v_withdrawal > v_balance THEN
    RAISE_APPLICATION_ERROR(-20001, 'Error: Withdrawal amount exceeds available balance.');
  END IF;
  
  DBMS_OUTPUT.PUT_LINE('Transaction processed successfully.');
  
EXCEPTION
  WHEN OTHERS THEN
    DBMS_OUTPUT.PUT_LINE(SQLERRM);
END;

In this Example:

• RAISE_APPLICATION_ERROR procedure raises error if the withdrawal amount exceeds the balance.
• The custom error message is being propagated along with the error code (-20001).

Custom Error Messages in PL/SQL

Using custom error messages in PL/SQL, one can provide useful, application-specific errors rather than rely on generic error messages implemented by Oracle. We use RAISE_APPLICATION_ERROR to raise custom exceptions with meaningful messages, and it gives us a clear idea about the problem, both from debugging and from user experience perspectives.

Example of Custom Error Messages

DECLARE
  v_emp_id NUMBER := 101;
BEGIN
  -- Simulating a business rule violation
  IF v_emp_id > 100 THEN
    RAISE_APPLICATION_ERROR(-20002, 'Error: Employee ID cannot be greater than 100.');
  END IF;

EXCEPTION
  WHEN OTHERS THEN
    DBMS_OUTPUT.PUT_LINE(SQLERRM);
END;

This example raises an application-specific error when the employee ID exceeds 100, allowing for clearer error handling related to business logic.

Oracle PL/SQL Error Management Best Practices

Proper management of errors in PL/SQL helps you make more robust, maintainable, and user-friendly applications. Here are some best practices about how to manage exceptions in PL/SQL:

• Use Specific Exception Handlers: Handle specific exceptions before you use the WHEN OTHERS clause. This way, you can give meaningful responses to specific error conditions.
• Log Errors: Always log exceptions to help with diagnosing and fixing problems later. This can be done by logging the error message and code in a database table or a log file.
• Avoid Silent Failures: Never let silent failures happen. Avoid simply preventing errors from appearing without notification to the ultimate end-user or developer. Every single error should be either logged or be communicated to the final end-user in order to avoid silent failures.
• Custom Error Codes and Messages: Employ RAISE_APPLICATION_ERROR to create custom error codes and messages thus explicit business logic violation would be given crystal clear, understandable meanings.
• Code Does Not Stop: Even after an exception has occurred, make sure that your program recovers gracefully or terminates in a controlled manner.

Table: Common Scenarios for Using RAISE vs RAISE_APPLICATION_ERROR

Scenario	RAISE	RAISE_APPLICATION_ERROR
Raise a custom exception for business logic violations	Yes	Yes
Raise predefined Oracle exceptions	Yes	No
Customize error messages and codes	No	Yes
Use for application-specific logic	Yes	Yes
Preserves original Oracle error codes	No	Optional (with keep_errors parameter)

Examples of RAISE and RAISE_APPLICATION_ERROR in PL/SQL

Example 1: Raising a User-Defined Exception

DECLARE
  insufficient_stock EXCEPTION;
  v_stock NUMBER := 5;
  v_requested_stock NUMBER := 10;
BEGIN
  IF v_requested_stock > v_stock THEN
    RAISE insufficient_stock;
  END IF;
  
  DBMS_OUTPUT.PUT_LINE('Stock is available for the order.');
  
EXCEPTION
  WHEN insufficient_stock THEN
    DBMS_OUTPUT.PUT_LINE('Error: Not enough stock to fulfill the order.');
END;

Example 2: Using RAISE_APPLICATION_ERROR for Custom Error Messages

DECLARE
  v_total_sales NUMBER := 50000;
BEGIN
  IF v_total_sales < 100000 THEN
    RAISE_APPLICATION_ERROR(-20003, 'Error: Total sales must be at least 100,000.');
  END IF;
  
  DBMS_OUTPUT.PUT_LINE('Sales target achieved.');
  
EXCEPTION
  WHEN OTHERS THEN
    DBMS_OUTPUT.PUT_LINE('An error occurred: ' || SQLERRM);
END;

Example 3: Using RAISE_APPLICATION_ERROR with keep_errors

BEGIN
  -- Some operation that could fail
  UPDATE employees SET salary = salary / 0;  -- Division by zero

EXCEPTION
  WHEN OTHERS THEN
    -- Preserve the original error and raise a custom one
    RAISE_APPLICATION_ERROR(-20004, 'Custom error: Division by zero occurred.', TRUE);
END;

Advantages of RAISE and RAISE_APPLICATION_ERROR in PL/SQL

RAISE and RAISE_APPLICATION_ERROR commands in PL/SQL: Both commands are significant tools for handling as well as raising custom exceptions within the programs. The resultant output helps control the flow of execution during error conditions and improves the reliability of the overall code. Below are the key advantages of using these commands in PL/SQL:

1. Improved Error Reporting

The RAISE_APPLICATION_ERROR function allows developers to raise user-defined exceptions along with custom error messages and error codes. This gives much more meaningful feedback not only to the user but also to calling programs, helping to explain the cause of the error in way that makes sense.

2. Greater control over exceptions

A RAISE statement makes it explicitly possible for the developer to raise any exception. It allows developers to raise predefined or user-defined exceptions at any point in a program; hence, it provides for fine control over when and where an error is raised, so the code will be more predictable and easier to manage.

3. Customisation Error Messages

Developers can write very detailed, context-specific error messages with RAISE_APPLICATION_ERROR; moreover, in such a message, they can integrate dynamic information concerning the state of the program, which may become critical for debugging and resolving the error.

4. Maintainability and Readability

With RAISE and RAISE_APPLICATION_ERROR, there is a way for developers to write clearer and more maintainable code. And there is no such thing as the waterfalls or the ambiguous propagation of the error by cascading it since the intention of throwing errors helps reorganise the flow of the program in a manner that would make it easier in reading and maintenance.

5. Structured Error Handling

RAISE and RAISE_APPLICATION_ERROR enable structured error handling; therefore, the exception will be taken care of in an appropriate method. This shall not increase a possibility of silent failures or unexpected failures since the programme could catch and handle the exception according to the defined logic.

6. Propagation of Errors

The RAISE command allows exceptions to propagate up the call stack, so that higher-level error handlers or calling procedures can take control of the exception. This is particularly helpful in multilayered applications where low-level functions might raise errors that need to be treated by higher-level systems.

7. Better Debugging

RAISE_APPLICATION_ERROR gives useful information during the debugging cycle. Errors that are being thrown are documented with custom messages and error codes. This eliminates guessing and provides a way to identify and solve problems quickly and easily in the code.

8. Granularity in Error Management

Using RAISE_APPLICATION_ERROR, developers can specify very specific error conditions based on one or more particular business rules or application logic. Thus, error handling becomes of a much more finer grain and meaningful, bringing about an added robustness to the application.

9. Enforcing Business Logic

But RAISE_APPLICATION_ERROR can be used to enforce business rules at database level: for example, if some operation violates business rule, it will raise a custom error with a clear explanation of the message, and thus such invalid data operations will not occur, and data will be intact.

10. Standard Error Codes

The RAISE_APPLICATION_ERROR function gives developers the ability to use a standard set of error codes (ranging from -20000 to -20999). This is helpful in maintaining uniformity within the application, thus it is easier to identify the nature of those errors. Furthermore, every error code will be unique and traceable.

Disadvantages of RAISE and RAISE_APPLICATION_ERROR in PL/SQL

While the RAISE and RAISE_APPLICATION_ERROR statements in PL/SQL provide extremely valuable benefits in working with errors, they are not without disadvantages and challenges developers should be concerned with. Some of these key disadvantages are summarized below:

1. Performance Overhead

For example, raising an exception, especially using RAISE_APPLICATION_ERROR, may come with performance overhead. Each time PL/SQL raises an exception, it will leave the normal flow of execution and begin to follow the error-handling process, and hence slow the performance down, especially if there are frequent occurrences of exceptions.

2. Complexity Enhancement

Overuse of RAISE and RAISE_APPLICATION_ERROR brings in unnecessary complexity to code in the codebase. Managing numerous custom exceptions and error codes makes code harder to be maintained, especially in large systems where errors need to be handled at multiple layers.

3. Toughness in Debugging Silent Errors

If RAISE or RAISE_APPLICATION_ERROR is not called through proper error-handling mechanisms (like EXCEPTION blocks), then the raised exceptions might not be logged and propagated properly. This can lead to silent errors that are hard to debug and trace.

4. Non-Standard Error Codes

The RAISE APPLICATION ERROR function uses a predefined range of error codes (-20000 to -20999), which is nonstandard compared with Oracle’s predefined error codes. Thus, one of the potential disadvantages of this approach is that it becomes tough, at the time of debugging, to separate between system errors and application-specific errors.

5. Overuse of Custom Errors

Overuse of RAISE_APPLICATION_ERROR for raising custom exceptions can cause undue fragmentation of the error management logic, leading to unmanageable proliferation of unique error codes and error messages-the nightmare of developers to track and standardize error handling across the system.

6. Disrupting Program Flow

Raising an exception interrupts normal program flow, which is not always preferred. Sometimes exceptions let the process end prematurely and cause some kind of part-way transactions or operations. This may lead to inconsistent states, especially if only err-handling mechanisms are implemented.

7. needs to be followed by Thorough Exception Handling

The exception handling with RAISE and RAISE_APPLICATION_ERROR has to be more elaborate so that errors can be dealt with in a proper way. In the worst scenario, the program may just crash, or some of the operations will remain in a partly processed state when exceptions are not handled properly.

8. Risk of Misuse

If RAISE_APPLICATION_ERROR is misused by raising exceptions for non-critical situations, then confusion will be created. It will make developers raise errors where a simple conditional can handle the situation with less complex logic, thereby making the maintenance burden heavier.

9. Multiple Source of Errors Not Feasible for Control

Whenever a number of custom exceptions are thrown through RAISE_APPLICATION_ERROR, it is not feasible to manage all of those customised error codes and makes sure that all of them log properly and get noticed. It might become quite difficult for the developers to track which errors belong to which part of the application. This will lead to misconceptions.