I'm expecting an error here since X_TEST column doesn't exists.
But the error is not being caught by the exception block.
BEGIN TRY
SELECT X_TEST FROM ACCOUNTS
END TRY
BEGIN CATCH
PRINT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
Why ? Is it because of the severity of the error ?
No, TRY can only handle certain types of errors within its own scope. Now, you say you have a stored procedure that looks like this (after non_existent_column has been dropped):
CREATE PROCEDURE dbo.blat
AS
BEGIN
BEGIN TRY
SELECT non_existent_column FROM dbo.table_that_exists;
END TRY
BEGIN CATCH
PRINT ERROR_MESSAGE();
END CATCH
END
GO
If you simply do this...
EXEC dbo.blat;
...you will get hammered with a compilation error because the statement within that TRY's scope fails to parse:
Msg 207, Level 16, State 1, Procedure fooblat, Line 5
Invalid column name 'non_existent_column'.
However you can catch this error at an outer scope (whether the procedure has TRY/CATCH or not):
BEGIN TRY
EXEC dbo.fooblat;
END TRY
BEGIN CATCH
PRINT 'There was an error:';
PRINT ERROR_MESSAGE();
END CATCH
Result (notice this is not an exception and the text is no longer red):
There was an error:
Invalid column name 'non_existent_column'.
You can also avoid this with dynamic SQL, but it seems like you've already shot that down, so this is the next best suggestion I can think of - capture the error at an outer scope.
It is a syntax error to use a non-existing column. Your batch never even starts to execute.
Consider this code:
BEGIN TRY
sdgedtju§$%&/()=
END TRY
BEGIN CATCH
PRINT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
You would not expect it to even start, right? It does not compile. Using a non-existing column is just the same
This code would give you the behavior you were expecting to see...
BEGIN TRY
exec('SELECT X_TEST FROM ACCOUNTS')
END TRY
BEGIN CATCH
PRINT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
Related
We are converting from Crystal to SSRS. In our stored procedures we have an outer TRY CATCH and can have many other TRY CATCH blocks. If there is an error or no data is found, a variable will be set with a message then the outer CATCH will display it.
It's something like this:
BEGIN TRY
BEGIN TRY
do stuff
END TRY
BEGIN CATCH
SET #ERROR_MSG = 'ERROR: There was a problem doing this. (' + ERROR_MESSAGE()) + ')'
RAISERROR (#ERROR_MSG, 11, 1)
END CATCH
IF NO DATA IS FOUND
BEGIN
SET #ERROR_MSG = 'No data was found'
RAISERROR (#ERROR_MSG, 11, 1)
END
SELECT DATA
RETURN 0
END TRY
BEGIN CATCH
SELECT #ERROR_MSG
RAISERROR (#ERROR_MSG, 11, 1)
RETURN 1
END CATCH
This has worked fine in Crystal, the error/no data found message displays correctly. In SSRS the RAISERROR in the CATCH is causing SSRS to display the error rsErrorReadingNextDataRow instead of the message.
If I comment out RAISERROR or use severity level 0-9 it works fine.
Is there any way I can use severity level 11 and have SSRS display the error message instead of the rsErrorReadingNextDataRow error? Thanks!
I would like to know the best position of a TRY/CATCH for a T-SQL procedure and why
In the statement:
CREATE PROCEDURE procedure_name
AS
BEGIN
-- Code
BEGIN TRY
sql_statement
END TRY
BEGIN CATCH
-- Handle errors
END CATCH
--Code
END
or in the call:
BEGIN TRY
EXEC procedure_name
END TRY
BEGIN CATCH
-- Handle errors
END CATCH
I would go for the first option.
BEGIN TRY
sql_statement
END TRY
BEGIN CATCH
-- Handle errors
END CATCH
The reason is you would want to catch the errors at the source and then take some appropriate actions.
In second option you are letting the error bubble up and there you would not have access to all the Exact error information returned by the error functions inside the catch block.
For example the ERROR_LINE() function will return the line number of the calling procedure where the it is calling the procedure containing the actual sql code, you would want to know the error line number where the actual exception was thrown, this information is only available in the catch block of the procedure being called.
Moral of the story is try to catch exceptions as close to the source as possible.
I have a stored procedure spMyProc. The procedure is passed a table name as a parameter #TableName. It is important to verify that the table exists before proceeding to the body of the procedure.
How can I create a custom exception to raise an error if the table name is invalid?
I am aware of TRY and CATCH but I'm unsure how to put this together with custom exceptions.
Regards.
Look into RAISERROR() funiction.
TRY.. CATCH works pretty same as it would work in any other programming language
BEGIN TRY
-- do your checks
IF NOT EXISTS(SELECT 1 FROM sys.tables WHERE NAME = #TableName)
BEGIN
RAISERROR('Table does not exist', 16,1)
END
-- rest of the code if checks are passed
-- if above checks are not passed and you riase an error
-- control will skip any code in TRY Block after the error has been
-- Raised and staright jump to Catch block.
END TRY
BEGIN CATCH
-- Do your error logging
-- Other stuff
-- you have access to ERROR_ functions here to get detailed info about errors
END CATCH
I think one of examples supplied here RAISERROR should match your problem. New versions of SQL Server will use THROW instead of RAISERROR.
You can use try catch and raiseerror for handle the custom exception, for example:
begin try
--sql statements
end try
begin catch
RAISERROR
(
ERROR_MESSAGE(), -- or add your custom message
ERROR_SEVERITY(),
1,
ERROR_NUMBER(), -- parameter: original error number.
ERROR_SEVERITY(), -- parameter: original error severity.
ERROR_STATE(), -- parameter: original error state.
ISNULL(ERROR_PROCEDURE(), '-'), -- parameter: original error procedure name.
ERROR_LINE() -- parameter: original error line number.
end catch
So in Sql Server it appears that I cannot have specific steps within my catch branch like I can in PL/SQL (I could add IF / ELSE checks).
So in PL/SQL I would have something like this
DECLARE
MY_EXCEPTION EXCEPTION;
BEGIN
//My Error is Raised
EXCEPTION
WHEN MY_EXCEPTION THEN
//Perform actions
END
How are others handling this? Is there a more elegant solution with the TRY / CATCH than using IF Statements to look at the errors and perform operations?
Thanks,
S
What kind of operations? Do you mean you want to declare elsewhere that for exception A it gets logged and exception B just gets ignored, and have your catch block inherit those actions? SQL Server 2012 adds THROW so that you can do other things (log, send e-mail, whatever) and then essentially re-throw the error that triggered the catch in the first place - but there is no way to define error handling as such centrally unless you pass the error number, severity etc. to a stored procedure (then the logic could be done in the procedure instead of in the CATCH block). Quick example:
CREATE PROCEDURE dbo.CustomErrorHandler
#ErrorNumber INT,
#ProcID INT
AS
BEGIN
IF #ErrorNumber = 8134
BEGIN
PRINT 'Oh, it was just divide by 0 in '
+ COALESCE(OBJECT_NAME(#ProcID), 'ad hoc');
RETURN;
END
IF #ErrorNumber = 208
BEGIN
PRINT 'Invalid object access!';
-- send e-mail about invalid object access
RETURN;
END
/* other custom handling for other exceptions */
RAISERROR('Unhandled exception I guess?', 11, 1);
END
GO
Then you could play with various exceptions (well, ones that pass the parsing phase, at least):
BEGIN TRY
SELECT 1/0; --8134
--EXEC('SELECT * FROM splunge;'); --208
END TRY
BEGIN CATCH
DECLARE
#e INT = ERROR_NUMBER(),
#p INT = ##PROCID;
EXEC dbo.CustomErrorHandler #e, #p;
END CATCH
For the bible on error handling see Erland's articles http://www.sommarskog.se/error-handling-I.html, http://www.sommarskog.se/error-handling-II.html and http://www.sommarskog.se/error_handling_2005.html
In the most recent SQL Servers you can use try catch blocks like:
BEGIN try
the code
END try
BEGIN catch
do whatever you need to do in case of exception
END catch
In older versions you are stuck with
IF ##ERROR > 0 THEN BEGIN
do you stuff
END IF
I am using SQL Server 2008 and when I run this Statement in Management studio the Select statement in the Catch Block is executed as expected
BEGIN TRY
INSERT INTO IDontExist(ProductID)
VALUES(1)
END TRY
BEGIN CATCH
SELECT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
However when I run this statement the statement in the Catch Block is never executed and instead the error is just displayed in the results tab
BEGIN TRY
Select * from IDontExist
END TRY
BEGIN CATCH
SELECT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
They both return the same error number '208' 'Invalid Object Name: IDontExist' so why would one get handled and the other not?
I don't get the CATCH block hit at all.
That's because the code won't compile, because the object doesn't exist, no plan is generated, so nothing runs to hit the CATCH block.
You can never hit this catch block so somethign is wrong with your testing/example. You can hit an outer catch block in a different scope (eg nested stored procs)
Edit: I'm using SQL Server 2005 SP3
It depends when deferred name resolution applies, related to statement level recompilation.
In my case, the whole batch fails both times and no statement level recompilation happens so no deferred name resolution
In OP's case, the batch compiles and runs but then has a statement level recompilation/deferred name resolution error in running code
I'm off to find some references about why it's different, given BOL doesn't say much, neither does Erland Sommarskog
This has bitten me in the past as well.
Not all errors generated inside the TRY block statements are passed into the CATCH block. Any errors with a severity of 10 or less are considered to be warnings and do not cause control to flow to the CATCH block. Also, any errors that break the database connection will not cause the CATCH block to be reached. There may be other situations as well.
Directly from http://msdn.microsoft.com/en-us/library/ms175976.aspx.
USE AdventureWorks2008R2;
GO
BEGIN TRY
-- Table does not exist; object name resolution
-- error not caught.
SELECT * FROM NonexistentTable;
END TRY
BEGIN CATCH
SELECT
ERROR_NUMBER() AS ErrorNumber
,ERROR_MESSAGE() AS ErrorMessage;
END CATCH
The error is not caught and control passes out of the TRY…CATCH construct to the next higher level.
Running the SELECT statement inside a stored procedure will cause the error to occur at a level lower than the TRY block. The error will be handled by the TRY…CATCH construct.
This behaviour happens if you previously had a table IDontExist and compiled a plan for it that is still in the cache then drop the table.
It also happens if you run the individual statement twice even without the table ever existing. The first run raises an error that is not caught. The second run (after the first plan is cached) succeeds.
/*Clear Cache*/
DBCC FREEPROCCACHE
GO
BEGIN TRY
INSERT INTO IDontExist(ProductID)
VALUES(1)
END TRY
BEGIN CATCH
SELECT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
GO
/*Plan now Cached*/
SELECT query_plan
FROM sys.dm_exec_cached_plans cp
OUTER APPLY sys.dm_exec_sql_text(plan_handle) t
OUTER APPLY sys.dm_exec_query_plan(plan_handle) qp
WHERE t.text LIKE '%IDontExist%'
OPTION (RECOMPILE)
GO
BEGIN TRY
INSERT INTO IDontExist(ProductID)
VALUES(1)
END TRY
BEGIN CATCH
SELECT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
GO
The INSERT statement gets auto parameterised.
If you change your Select * from IDontExist statement to Select * from IDontExist WHERE ProductID = 1 this also becomes auto parameterised and they behave the same.
I'm not absolutely certain why the auto parameterisation makes a difference here. I think that it is explained by the below extract from BOL however.
The following types of errors are not handled by a CATCH block when they occur at the same level of execution as the TRY…CATCH construct ... [those] that occur during statement-level recompilation ... If an error occurs during compilation or statement-level recompilation at a lower execution level (for example, when executing sp_executesql or a user-defined stored procedure) inside the TRY block, the error
occurs at a lower level than the TRY…CATCH construct and will be handled by the associated CATCH block.
I presume the auto parametrization of that statement means that it gets recompiled at a lower execution level and is catchable.
Now that we have all the explanations as to why this is happening. Let's see an actual solution to the problem.
First let's take the statements that #d-k-mulligan proposed above and turn them into stored procs.
IF OBJECT_ID('dbo.prcIDontExistINSERT', 'P') IS NOT NULL DROP PROCEDURE dbo.prcIDontExistINSERT
GO
CREATE PROCEDURE dbo.prcIDontExistINSERT
AS
BEGIN TRY
INSERT INTO IDontExist(ProductID)
VALUES(1)
END TRY
BEGIN CATCH
SELECT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
GO
IF OBJECT_ID('dbo.prcIDontExistSELECT', 'P') IS NOT NULL DROP PROCEDURE dbo.prcIDontExistSELECT
GO
CREATE PROCEDURE dbo.prcIDontExistSELECT
AS
BEGIN TRY
SELECT * FROM IDontExist
END TRY
BEGIN CATCH
SELECT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
GO
If we run either of them we see the same error.
EXEC dbo.prcIDontExistINSERT
EXEC dbo.prcIDontExistSELECT
Msg 208, Level 16, State 1, Procedure prcIDontExistSELECT, Line 4
Invalid object name 'IDontExist'.
The solution now is to create error handling wrapper procs with the sole purpose of catching any error from the original procs above that are getting the object not found errors.
IF OBJECT_ID('dbo.prcIDontExistInsert_ERROR_HANDLER', 'P') IS NOT NULL DROP PROCEDURE dbo.prcIDontExistInsert_ERROR_HANDLER
GO
CREATE PROCEDURE dbo.prcIDontExistInsert_ERROR_HANDLER
AS
BEGIN TRY
EXEC dbo.prcIDontExistINSERT
END TRY
BEGIN CATCH
SELECT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
GO
IF OBJECT_ID('dbo.prcIDontExistSELECT_ERROR_HANDLER', 'P') IS NOT NULL DROP PROCEDURE dbo.prcIDontExistSELECT_ERROR_HANDLER
GO
CREATE PROCEDURE dbo.prcIDontExistSELECT_ERROR_HANDLER
AS
BEGIN TRY
EXEC dbo.prcIDontExistSELECT
END TRY
BEGIN CATCH
SELECT 'There was an error! ' + ERROR_MESSAGE()
END CATCH
GO
Finally, let's run either of our error handling procs and see the message we expect.
EXEC dbo.prcIDontExistInsert_ERROR_HANDLER
EXEC dbo.prcIDontExistSELECT_ERROR_HANDLER
There was an error! Invalid object name 'IDontExist'.
NOTE: Kalman Toth did all the hard research work here:
http://www.sqlusa.com/articles2008/trycatch/
Workaround with dynamic sql. Maybe it will be helpful for someone.
begin try
exec('
insert into IDontExist(ProductID)
values(1)
')
end try
begin catch
select 'There was an error! ' + error_message()
end catch