How to add a Try/Catch to SQL Stored Procedure
See TRY...CATCH (Transact-SQL)
CREATE PROCEDURE [dbo].[PL_GEN_PROVN_NO1]
@GAD_COMP_CODE VARCHAR(2) =NULL,
@@voucher_no numeric =null output
AS
BEGIN
begin try
-- your proc code
end try
begin catch
-- what you want to do in catch
end catch
END -- proc end
Transact-SQL is a bit more tricky that C# or C++ try/catch blocks, because of the added complexity of transactions. A CATCH block has to check the xact_state() function and decide whether it can commit or has to rollback. I have covered the topic in my blog and I have an article that shows how to correctly handle transactions in with a try catch block, including possible nested transactions: Exception handling and nested transactions.
create procedure [usp_my_procedure_name]
as
begin
set nocount on;
declare @trancount int;
set @trancount = @@trancount;
begin try
if @trancount = 0
begin transaction
else
save transaction usp_my_procedure_name;
-- Do the actual work here
lbexit:
if @trancount = 0
commit;
end try
begin catch
declare @error int, @message varchar(4000), @xstate int;
select @error = ERROR_NUMBER(),
@message = ERROR_MESSAGE(), @xstate = XACT_STATE();
if @xstate = -1
rollback;
if @xstate = 1 and @trancount = 0
rollback
if @xstate = 1 and @trancount > 0
rollback transaction usp_my_procedure_name;
raiserror ('usp_my_procedure_name: %d: %s', 16, 1, @error, @message) ;
return;
end catch
end
Error-Handling with SQL Stored Procedures
TRY/CATCH error handling can take place either within or outside of a procedure (or both). The examples below demonstrate error handling in both cases.
If you want to experiment further, you can fork the query on Stack Exchange Data Explorer.
(This uses a temporary stored procedure... we can't create regular SP's on SEDE, but the functionality is the same.)
--our Stored Procedure
create procedure #myProc as --we can only create #temporary stored procedures on SEDE.
begin
BEGIN TRY
print 'This is our Stored Procedure.'
print 1/0 --<-- generate a "Divide By Zero" error.
print 'We are not going to make it to this line.'
END TRY
BEGIN CATCH
print 'This is the CATCH block within our Stored Procedure:'
+ ' Error Line #'+convert(varchar,ERROR_LINE())
+ ' of procedure '+isnull(ERROR_PROCEDURE(),'(Main)')
--print 1/0 --<-- generate another "Divide By Zero" error.
-- uncomment the line above to cause error within the CATCH ¹
END CATCH
end
go
--our MAIN code block:
BEGIN TRY
print 'This is our MAIN Procedure.'
execute #myProc --execute the Stored Procedure
--print 1/0 --<-- generate another "Divide By Zero" error.
-- uncomment the line above to cause error within the MAIN Procedure ²
print 'Now our MAIN sql code block continues.'
END TRY
BEGIN CATCH
print 'This is the CATCH block for our MAIN sql code block:'
+ ' Error Line #'+convert(varchar,ERROR_LINE())
+ ' of procedure '+isnull(ERROR_PROCEDURE(),'(Main)')
END CATCH
Here's the result of running the above sql as-is:
This is our MAIN Procedure.
This is our Stored Procedure.
This is the CATCH block within our Stored Procedure: Error Line #5 of procedure #myProc
Now our MAIN sql code block continues.
¹ Uncommenting the "additional error line" from the Stored Procedure's CATCH block will produce:
This is our MAIN procedure.
This is our Stored Procedure.
This is the CATCH block within our Stored Procedure: Error Line #5 of procedure #myProc
This is the CATCH block for our MAIN sql code block: Error Line #13 of procedure #myProc
² Uncommenting the "additional error line" from the MAIN procedure will produce:
This is our MAIN Procedure.
This is our Stored Pprocedure.
This is the CATCH block within our Stored Procedure: Error Line #5 of procedure #myProc
This is the CATCH block for our MAIN sql code block: Error Line #4 of procedure (Main)
Use a single procedure for error handling
On topic of stored procedures and error handling, it can be helpful (and tidier) to use a single, dynamic, stored procedure to handle errors for multiple other procedures or code sections.
Here's an example:
--our error handling procedure
create procedure #myErrorHandling as
begin
print ' Error #'+convert(varchar,ERROR_NUMBER())+': '+ERROR_MESSAGE()
print ' occurred on line #'+convert(varchar,ERROR_LINE())
+' of procedure '+isnull(ERROR_PROCEDURE(),'(Main)')
if ERROR_PROCEDURE() is null --check if error was in MAIN Procedure
print '*Execution cannot continue after an error in the MAIN Procedure.'
end
go
create procedure #myProc as --our test Stored Procedure
begin
BEGIN TRY
print 'This is our Stored Procedure.'
print 1/0 --generate a "Divide By Zero" error.
print 'We will not make it to this line.'
END TRY
BEGIN CATCH
execute #myErrorHandling
END CATCH
end
go
BEGIN TRY --our MAIN Procedure
print 'This is our MAIN Procedure.'
execute #myProc --execute the Stored Procedure
print '*The error halted the procedure, but our MAIN code can continue.'
print 1/0 --generate another "Divide By Zero" error.
print 'We will not make it to this line.'
END TRY
BEGIN CATCH
execute #myErrorHandling
END CATCH
Example Output: (This query can be forked on SEDE here.)
This is our MAIN procedure.
This is our stored procedure.
Error #8134: Divide by zero error encountered.
occurred on line #5 of procedure #myProc
*The error halted the procedure, but our MAIN code can continue.
Error #8134: Divide by zero error encountered.
occurred on line #5 of procedure (Main)
*Execution cannot continue after an error in the MAIN procedure.
Documentation:
In the scope of a TRY/CATCH block, the following system functions can be used to obtain information about the error that caused the CATCH block to be executed:
ERROR_NUMBER()returns the number of the error.ERROR_SEVERITY()returns the severity.ERROR_STATE()returns the error state number.ERROR_PROCEDURE()returns the name of the stored procedure or trigger where the error occurred.ERROR_LINE()returns the line number inside the routine that caused the error.ERROR_MESSAGE()returns the complete text of the error message. The text includes the values supplied for any substitutable parameters, such as lengths, object names, or times.
(Source)
Note that there are two types of SQL errors: Terminal and Catchable. TRY/CATCH will [obviously] only catch the "Catchable" errors. This is one of a number of ways of learning more about your SQL errors, but it probably the most useful.
It's "better to fail now" (during development) compared to later because, as Homer says . . .
