1. 2015 International TechNet Wiki Summit 2015 Saeid Hasani Structured Error Handling Mechanism in SQL Server 2012 & 2014

2. Senior Database Developer SQL Server Consultant Freelance SQL Author T-SQL Trainer Technet and MSDN SQL Server Forums Moderator 2 Saeid Hasani

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4. TRY Try executing statements CATCH Handle the errors if they occur 4 Is there any structured Error Handling mechanism in SQL Server?

5. 5 BEGIN TRY -- Start to try executing statements SELECT 1 / 0; /* Executing statements */ END TRY -- End of trying to execute statements BEGIN CATCH -- Start to Handle the error if occurs PRINT 'Error occurs!' /* Handle the error */ END CATCH -- End of Handling the error if occurred

6. Is there any structured Error Handling mechanism in SQL Server? 6

7. Will all statements in TRY block try to execute? BEGIN TRY -- Start to try executing statements PRINT 'Before Error!' -- Statement no1 SELECT 1 / 0; -- Statement no2 PRINT 'After Error!' -- Statement no3 END TRY -- End of trying to execute statements BEGIN CATCH -- Start to Handle the error if occurs PRINT 'Error occurs!' /* Handle the error */ END CATCH -- End of Handling the error if occurred 7

8. Will all statements in TRY block try to execute? 8

9. Does the CATCH part automatically handle the errors? BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- Statement END TRY -- End of trying to execute statements BEGIN CATCH -- Start to Handle the error if occurs END CATCH -- End of Handling the error if occurred 9

10. Does the CATCH part automatically handle the errors? 10

11. Does the CATCH part automatically handle the errors? TRY Try executing statements CATCH Handle the error if occurs RAISERROR 11

12. Does the CATCH part automatically handle the errors? BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- Statement END TRY -- End of trying to execute statements BEGIN CATCH -- Start to Handle the error if occurs RAISERROR('Error!!!', 16, 1); END CATCH -- End of Handling the error if occurred 12

13. Does the CATCH part automatically handle the errors? 13

14. Does the CATCH part automatically handle the errors? TRY Try executing statements CATCH Handle the error if occurs RAISERROR ERROR_NUMBER() ERROR_MESSAGE() ERROR_SEVERITY() ERROR_STATE() ERROR_PROCEDURE() ERROR_LINE() 14

15. Does the CATCH part automatically handle the errors? BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- Statement END TRY -- End of trying to execute statements BEGIN CATCH -- Start to Handle the error if occurs DECLARE @ErrorMessage NVARCHAR(4000); DECLARE @ErrorSeverity INT; DECLARE @ErrorState INT; SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY(), @ErrorState = ERROR_STATE(); RAISERROR (@ErrorMessage, -- Message text. @ErrorSeverity, -- Severity. @ErrorState -- State. ); END CATCH -- End of Handling the error if occurred 15

16. Does the CATCH part automatically handle the errors? 16

17. Is it a good idea to use a general procedure as a modular Error Handler routine? CREATE PROCEDURE spErrorHandler AS SET NOCOUNT ON; DECLARE @ErrorMessage NVARCHAR(4000); DECLARE @ErrorSeverity INT; DECLARE @ErrorState INT; SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY(), @ErrorState = ERROR_STATE(); RAISERROR (@ErrorMessage, -- Message text. @ErrorSeverity, -- Severity. @ErrorState -- State. ); 17

18. Is it a good idea to use a general procedure as a modular Error Handler routine? CREATE PROCEDURE spTest AS SET NOCOUNT ON; BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- Statement END TRY -- End of trying to execute statements BEGIN CATCH -- Start to Handle the error if occurs EXEC spErrorHandler; END CATCH -- End of Handling the error if occurred go ------------ EXEC spTest 18

19. Is it a good idea to use a general procedure as a modular Error Handler routine? 19

20. Is it a good idea to use a general procedure as a modular Error Handler routine? CREATE PROCEDURE spTest AS SET NOCOUNT ON; BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- Statement END TRY -- End of trying to execute statements BEGIN CATCH -- Start to Handle the error if occurs DECLARE @ErrorMessage NVARCHAR(4000); DECLARE @ErrorSeverity INT; DECLARE @ErrorState INT; SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY(), @ErrorState = ERROR_STATE(); RAISERROR (@ErrorMessage, -- Message text. @ErrorSeverity, -- Severity. @ErrorState -- State. ); END CATCH -- End of Handling the error if occurred 20

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22. What are the benefits of THROW when we have RAISERROR? 22

23. 1. Correct line number of the error! CREATE PROCEDURE spTest AS SET NOCOUNT ON; BEGIN TRY SELECT 1/0 END TRY BEGIN CATCH declare @msg nvarchar(2000) = error_message(); raiserror( @msg, 16, 1); THROW END CATCH 23

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25. 2. Easy to use Another benefit of using the THROW statement is that there is no need for extra code in RAISERROR. 25

26. 3. Real Terminator! BEGIN CATCH DECLARE @msg NVARCHAR(2000) = ERROR_MESSAGE(); RAISERROR( @msg, 16, 1); ----------------------------- CREATE TABLE #Saeid (id INT) INSERT #Saeid VALUES ( 101 ); SELECT * FROM #Saeid; DROP TABLE #Saeid; ----------------------------- THROW PRINT 'This will never print!!!'; END CATCH 26

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28. 4. Independence of sys.messages 28 CREATE PROC sptest AS SET NOCOUNT ON; BEGIN TRY SELECT 1/0 END TRY BEGIN CATCH THROW 60000, 'This a custom message!', 1; END CATCH

29. 4. Independence of sys.messages 29

30. I want to check a condition in the TRY block. How can I control the flow of execution and raise the error? CREATE PROC sptest AS SET NOCOUNT ON; BEGIN TRY THROW 60000, 'This a custom message!', 1; END TRY BEGIN CATCH THROW END CATCH 30

31. I want to check a condition in the TRY block. How can I control the flow of execution and raise the error? 31

32. Does the CATCH part automatically rollback the statements within the TRY part? CREATE PROC sptest AS SET NOCOUNT ON; BEGIN TRY CREATE TABLE dbo.Saeid --No1 ( id int ); SELECT 1/0 --No2 END TRY BEGIN CATCH THROW END CATCH go -------------------------------------> 32 EXEC sptest; SELECT * FROM dbo.Saeid;

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34. Can someone use TRANSACTION in the TRY/CATCH block? CREATE PROC sptest AS SET NOCOUNT ON; BEGIN TRY SET XACT_ABORT ON; --set xact_abort option BEGIN TRAN --begin transaction CREATE TABLE dbo.Hasani ( id int ); SELECT 1/0 COMMIT TRAN --commit transaction END TRY BEGIN CATCH IF @@TRANCOUNT > 0 --check if there are open transaction? ROLLBACK TRAN; --rollback transaction THROW END CATCH -------------------------------------> 34 EXEC sptest; SELECT * FROM dbo.Saeid;

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36. Can someone use TRANSACTION in the TRY/CATCH block? TRY block XACT_ABORT Begin transaction Statements to try Commit transaction CATCH block Check @@TRANCOUNT and rollback all transactions THROW 36

37. See Also Related TechNet Wiki Articles: Error Handling within Triggers Using T-SQL T-SQL: Error Handling for CHECK Constraints BOL link: http://technet.microsoft.com/en-us/library/ms175976.aspx 37