How do you use TRY...CATCH blocks to control the flow of stored procedures?

1 What are TRY...CATCH blocks?

TRY...CATCH blocks are a pair of keywords that define a section of code that can potentially generate an error, and a section of code that can handle that error. The TRY block contains the main logic of your stored procedure, such as inserting, updating, deleting, or selecting data. The CATCH block contains the code that executes when an error occurs in the TRY block, such as rolling back transactions, logging errors, raising custom errors, or returning values.

2 How to use TRY...CATCH blocks?

Using TRY...CATCH blocks in your stored procedures requires you to start the TRY block with the keyword TRY and end it with the keyword END TRY, followed by starting the CATCH block with the keyword CATCH and ending it with the keyword END CATCH. Any code that can generate an error should be placed in the TRY block, such as SQL statements, dynamic SQL, or calls to other stored procedures. The CATCH block should contain code that can handle the error, like ROLLBACK TRANSACTION, PRINT, RAISERROR, or RETURN. As an example, a stored procedure may try to insert a new record into a table and handle any duplicate key errors by returning a custom error message.

3 What are the benefits of TRY...CATCH blocks?

TRY...CATCH blocks offer several advantages for controlling the flow of stored procedures. Instead of relying on @@ERROR or @@ROWCOUNT variables, they allow you to handle different types of errors in a consistent and centralized way. Furthermore, these blocks can preserve the original error information, such as the error number, message, severity, state, and procedure name. The RAISERROR function with a severity level of 11 to 19 can also be used to raise custom errors that provide more meaningful and user-friendly messages. Lastly, the RETURN statement or output parameters can be used to return values or parameters from the stored procedure, even when an error occurs.

4 What are the limitations of TRY...CATCH blocks?

TRY...CATCH blocks have certain limitations to be aware of, such as not catching all types of errors, like syntax or connection errors, or those with a severity level of 20 or higher. Furthermore, they do not handle nested transactions. To address these issues, you should consider validating input parameters, using SET XACT_ABORT ON, configuring SQL Server alerts, using event notifications, using savepoints, employing conditional logic, or avoiding nested transactions in the client application.

5 What are some best practices and tips for using TRY...CATCH blocks?

To use TRY...CATCH blocks effectively and efficiently, you can apply some best practices and tips. For example, it’s recommended to use a single TRY...CATCH block for the entire stored procedure, as it simplifies code and reduces overhead. Additionally, use a consistent and standard format for your TRY...CATCH blocks to improve readability and maintainability. Moreover, use the THROW statement instead of the RAISERROR function when possible to make code more concise and accurate. Lastly, use the XACT_STATE() function to check the state of the transaction before committing or rolling back in order to prevent errors or inconsistencies in your data.

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?