What are the advantages and disadvantages of using DB2 SIGNAL and RESIGNAL statements for error handling?

1 What are SIGNAL and RESIGNAL statements?

SIGNAL and RESIGNAL are SQL statements that allow you to raise and propagate user-defined errors or conditions. You can use them to implement custom logic, validation, or business rules in your SQL code. For example, you can use SIGNAL to abort a transaction if a certain condition is not met, or RESIGNAL to pass an error message to the calling program or procedure.

2 How to use SIGNAL and RESIGNAL statements?

To use SIGNAL or RESIGNAL, you need to specify a condition name and an optional SQLSTATE value. A condition name is a user-defined identifier that describes the error or condition. An SQLSTATE value is a five-character code that indicates the type and class of the error or condition. You can also provide additional information, such as a message text, a severity level, or a constraint name, using the SET clause.

For example, the following statement raises a user-defined error with the condition name INVALID_SALARY, the SQLSTATE value 45000 (unhandled user-defined exception), and a message text:

SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Salary cannot be negative';

The following statement re-raises the same error with a different message text:

RESIGNAL SET MESSAGE_TEXT = 'Invalid salary detected';

3 When to use SIGNAL and RESIGNAL statements?

SIGNAL and RESIGNAL statements are useful when you want to enforce your own rules or logic in your SQL code, or when you want to communicate specific information about an error or condition to the calling program or procedure. For example, you can use them to validate input data and reject invalid values, check business rules and constraints and report violations, handle exceptions and errors in stored procedures and functions, customize error messages and severity levels, and propagate user-defined errors or conditions to the caller.

4 What are the advantages of using SIGNAL and RESIGNAL statements?

Using SIGNAL and RESIGNAL statements can provide you with more control and flexibility over your error handling logic and behavior. You can create user-defined errors or conditions that are meaningful and relevant to your application or business domain, as well as provide more information and details about an error or condition, such as a message text, a severity level, or a constraint name. Additionally, these statements can make your SQL code more readable and maintainable by separating the error handling logic from the main logic.

5 What are the disadvantages of using SIGNAL and RESIGNAL statements?

Using SIGNAL and RESIGNAL statements in SQL code may introduce complexity and overhead, and may cause unexpected results if not handled properly or following SQL standard or DB2 conventions. Additionally, they may not be compatible or portable with other SQL dialects or database systems that do not support them or that implement them differently. Moreover, these statements may not be sufficient or appropriate for some error handling scenarios that require more advanced techniques, such as retrying, logging, or notifying.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?