Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

that exercises the trigger we most recently worked with in this chapter. We can then step into that script,
so we can watch the debugger run through it line by line:
BEGIN TRAN
-- This one should work
UPDATE Production.ProductInventory
SET Quantity = 400 -- Was 408 if you want to set it back
WHERE ProductID = 1
AND LocationID = 1
-- This one shouldn’t
UPDATE Production.ProductInventory
SET Quantity = 1 -- Was 408 if you want to set it back
WHERE ProductID = 1
AND LocationID = 1
IF @@TRANCOUNT > 0
ROLLBACK TRAN
With this script up in the Query Window in Management Studio, we can just press F11 to step into the
script (or set a breakpoint and then use any of the several options that start the debugger). We start, of
course, at the BEGIN TRAN statement. Continue to step into (F11) until you execute the first UPDATE
statement, and note that you wind up in the trigger. Figure 15-6 shows the call stack as you enter the
trigger for the first time.
Figure 15-6
Now, go ahead and step out of the first UPDATE, and into the second UPDATE. Since the first UPDATE
statement didn’t match the violation test in the trigger, you exited almost immediately, but this second
time you should see, as you step through, that the code that aborts the transaction fires.
In short, we were able to utilize a single script that, in this case, had two statements meant to test the
two possible code paths in our trigger. Obviously, you would need more complex scripting to handle the
possible code paths for more complex triggers, but, beyond that, the debugging needs are pretty much
as they are for testing any other code in T-SQL.
Summary
Chapter 15: Triggers
Triggers are an extremely powerful tool that can add tremendous flexibility to both your data integrity
and the overall operation of your system. That being said, they are not something to take lightly. Triggers
can greatly enhance the performance of your system if you use them for proper summarization of
data, but they can also be the bane of your existence. They can be very difficult to debug (even now that
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