I have a stored procedure that has a loop based on a counter. When the counter becomes NULL the loop ends without any error. Why doesn't SQL Server at least display a warning or error message like other programming languages?
Here is a code sample which exhibits the problem:
DECLARE #MasterCount int = 0;
DECLARE #Count int; -- initialized to NULL by SQL Server
PRINT 'Starting'
IF (#MasterCount IS NULL)
PRINT '#MasterCount IS NULL';
ELSE
PRINT '#MasterCount ' + CAST(#MasterCount AS varchar(10))
IF (#Count IS NULL)
PRINT '#Count IS NULL';
WHILE (#MasterCount IS NOT NULL)
BEGIN
SET #MasterCount += #Count;
IF ##ERROR <> 0 PRINT 'Error occured!'
PRINT 'Loop #Count ' + CAST(#Count AS varchar(10))
SET #Count -= 1;
END
IF ##ERROR <> 0 PRINT 'Error occured!'
IF (#MasterCount IS NULL)
PRINT '#MasterCount IS NULL';
ELSE
PRINT '#MasterCount ' + CAST(#MasterCount AS varchar(10))
PRINT 'Ending'
Produces the following output:
Starting
#MasterCount 0
#Count IS NULL
#MasterCount IS NULL
Ending
It doesn't raise an error because this is defined, documented behaviour.
If you have two apples and you know the weight of only one then it makes sense that the weight of both of them added together is not known.
You can actually get a warning to appear if you slightly alter the formulation.
Instead of
SET #MasterCount += #Count;
You could use
SELECT #MasterCount = SUM(C)
FROM (VALUES(#Count),
(#MasterCount )) V(C);
In which case it gives
Warning: Null value is eliminated by an aggregate or other SET
operation.
This does change the semantics however. As the null value was entirely ignored you would end up with #MasterCount simply being assigned back its original value rather than being set to null in your scenario.
We have a bunch of old stored procedures with legacy style error trapping. I changed one the other day and included a newer TRY...CATCH block. The stored procedure just stopped after the TRY/CATCH and returned as though there were an error in the legacy block.
If I put a
SELECT NULL
in between the two everything works fine. Anyone know why this is happening?
--BEGIN NEW ERROR TRAP--
BEGIN TRY
Do stuff...
END TRY
BEGIN CATCH
END CATCH
--END NEW ERROR TRAP---
----------------- OLD SCHOOL TRAP BEGIN -----------------
SELECT #spERROR = ##ERROR ,
#spROWCOUNT = ##ROWCOUNT
SET #spRETURN = #spRETURN + 1
IF ( #spROWCOUNT <= 0
OR #spERROR <> 0
)
SET #spRETURN = 0 - #spRETURN
IF ( #spROWCOUNT <= 0
OR #spERROR <> 0
)
RETURN #spRETURN
SELECT #spROWCOUNT = -1 ,
#spERROR = -1
------------------ OLD SCHOOL ERROR TRAP END ------------------
In your try catch block, the last statement is probably doing something that sets the row count to 0. The "SELECT NULL" is setting the row count to 1, since it returns one row, so no error is detected.
You can fix this by changing the logic in the "old" code or by setting your row count variable in the try/catch code. I would recommend that you remove the SELECT NULL, since it would guarantee success and you may not want that behavior.
I have the following T-SQL if statement:
if #changeType = 'ChangeFrom'
begin
print 'yep'
end
else
begin
print 'nope'
end
If #changeType = 'ChangeFrom' I get yep.
If #changeType = 'ChangeTo' I get nope.
If #changeType ='ChangeFromfsjkfh' I get yep! Whats going on there?
What length have you declared the #ChangeType variable as - it looks like it's getting truncated?
I have a simple query which loops and I want to see the PRINT messages during the execution. The query is something like this:
WHILE 1 = 1
BEGIN
WAITFOR DELAY '000:00:10'
PRINT 'here'
END
The PRINT 'here' does not output until I stop the process. However, I want to see it while it's running. Is this possible?
You can use RAISERROR with serverity 0 and the NOWAIT option
WHILE 1 = 1
BEGIN
WAITFOR DELAY '000:00:10'
RAISERROR ('here', 0, 1) WITH NOWAIT
END
I believe that the prints get buffered, releasing "chunks" as the buffer fills up.
try using raiserror:
How do I flush the PRINT buffer in TSQL?
Try this..
DECLARE #i INT = 1
WHILE ( #i <= 10)
BEGIN
--- do something
SELECT 'Completed ' + CAST(#i AS VARCHAR(50)) + ' : ' + CAST(GETDATE() AS VARCHAR(50));
SET #i = #i + 1
END
current suggestions don't work for SSMS 18 and above.
Print then raiserror(N'', 0, 1) seems to get around this.
I have a stored procedure that does some parameter validation and should fail and stop execution if the parameter is not valid.
My first approach for error checking looked like this:
create proc spBaz
(
#fooInt int = 0,
#fooString varchar(10) = null,
#barInt int = 0,
#barString varchar(10) = null
)
as
begin
if (#fooInt = 0 and (#fooString is null or #fooString = ''))
raiserror('invalid parameter: foo', 18, 0)
if (#barInt = 0 and (#barString is null or #barString = ''))
raiserror('invalid parameter: bar', 18, 0)
print 'validation succeeded'
-- do some work
end
This didn't do the trick since severity 18 doesn't stop the execution and 'validation succeeded' is printed together with the error messages.
I know I could simply add a return after every raiserror but this looks kind of ugly to me:
if (#fooInt = 0 and (#fooString is null or #fooString = ''))
begin
raiserror('invalid parameter: foo', 18, 0)
return
end
...
print 'validation succeeded'
-- do some work
Since errors with severity 11 and higher are caught within a try/catch block another approach I tested was to encapsulate my error checking inside such a try/catch block. The problem was that the error was swallowed and not sent to the client at all. So I did some research and found a way to rethrow the error:
begin try
if (#fooInt = 0 and (#fooString is null or #fooString = ''))
raiserror('invalid parameter: foo', 18, 0)
...
end try
begin catch
exec usp_RethrowError
return
end catch
print 'validation succeeded'
-- do some work
I'm still not happy with this approach so I'm asking you:
How does your parameter validation look like? Is there some kind of "best practice" to do this kind of checking?
I don't think that there is a single "right" way to do this.
My own preference would be similar to your second example, but with a separate validation step for each parameter and more explicit error messages.
As you say, it's a bit cumbersome and ugly, but the intent of the code is obvious to anyone reading it, and it gets the job done.
IF (ISNULL(#fooInt, 0) = 0)
BEGIN
RAISERROR('Invalid parameter: #fooInt cannot be NULL or zero', 18, 0)
RETURN
END
IF (ISNULL(#fooString, '') = '')
BEGIN
RAISERROR('Invalid parameter: #fooString cannot be NULL or empty', 18, 0)
RETURN
END
We normally avoid raiseerror() and return a value that indicates an error, for example a negative number:
if <errorcondition>
return -1
Or pass the result in two out parameters:
create procedure dbo.TestProc
....
#result int output,
#errormessage varchar(256) output
as
set #result = -99
set #errormessage = null
....
if <errorcondition>
begin
set #result = -1
set #errormessage = 'Condition failed'
return #result
end
I prefer to return out as soon an possible, and see not point to having everything return out from the same point at the end of the procedure. I picked up this habit doing assembly, years ago. Also, I always return a value:
RETURN 10
The application will display a fatal error on positive numbers, and will display the user warning message on negative values.
We always pass back an OUTPUT parameter with the text of the error message.
example:
IF ~error~
BEGIN
--if it is possible to be within a transaction, so any error logging is not ROLLBACK later
IF XACT_STATE()!=0
BEGIN
ROLLBACK
END
SET #OutputErrMsg='your message here!!'
INSERT INTO ErrorLog (....) VALUES (.... #OutputErrMsg)
RETURN 10
END
I always use parameter #Is_Success bit as OUTPUT. So if I have an error then #Is_success=0. When parent procedure checks that #Is_Success=0 then it rolls back its transaction(with child transactions) and sends error message from #Error_Message to client.
As you can see from this answer history I followed this question and accepted answer, and then proceeded to 'invent' a solution that was basically the same as your second approach.
Caffeine is my main source of energy, due to the fact that I spend most of my life half-asleep as I spend far too much time coding; thus I didn't realise my faux-pas until you rightly pointed it out.
Therefore, for the record, I prefer your second approach: using an SP to raise the current error, and then using a TRY/CATCH around your parameter validation.
It reduces the need for all the IF/BEGIN/END blocks and therefore reduces the line count as well as puts the focus back on the validation. When reading through the code for the SP it's important to be able to see the tests being performed on the parameters; all the extra syntactic fluff to satisfy the SQL parser just gets in the way, in my opinion.