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Errors in SQL are considered inevitable. They are bound to occur now and then as you’ll inevitably run into some roadblocks while querying your data. The good news is that SQL has a way of managing these errors. This post will guide you through understanding and handling errors in SQL.
Understanding SQL Errors
SQL errors usually occur when you mistype or misstructure your SQL commands, or when you attempt to process data that is inconsistent with your command. For instance, you may attempt to divide a number by zero, which is a mathematical error. Here’s an example using T-SQL:
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SELECT 12 / 0 |
The preceding SQL command will raise an error because you cannot divide a number by zero. So, how do we handle such an error?
Error Handling in SQL
In SQL, we handle errors using structured exception handling. In T-SQL, we do this using the TRY…CATCH feature. This means that we write our SQL commands inside a TRY block and then handle errors inside a CATCH block. If an error occurs inside the TRY block, control is passed to the corresponding CATCH block where the error is handled.
Error Handling with TRY…CATCH
Below is an example of how to use the TRY…CATCH feature in T-SQL:
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BEGIN TRY SELECT 12 / 0 END TRY BEGIN CATCH SELECT ERROR_NUMBER() AS ErrorNumber, ERROR_MESSAGE() AS ErrorMessage END CATCH |
In this example, the division by zero error is caught in the CATCH block and an error message is displayed. The ERROR_NUMBER() and ERROR_MESSAGE() functions return the number and the message of the error, respectively.
Conclusion
In SQL, error management is a crucial aspect of writing and executing queries. Exception handling techniques such as TRY…CATCH in T-SQL allows you to catch and process errors effectively, providing valuable feedback and preventing your application from fatal crashes.