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

Chapter 11: Writing Scripts and Batches
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exit the TRY block immediately and begin with the first line in your CATCH block. Since there are more
possible error levels than just 11–19, take a look at what we have there:
Error Level Nature
1–10 Informational only. This would include things like context changes such as settings
being adjusted or NULL values found while calculating aggregates. These
will not trigger a CATCH block, so if you need to test for this level of error, you’ll
need to do so manually by checking @@ERROR.
11–19 Relatively severe errors, but ones that can be handled by your code (foreign key
violations, as an example). Some of these can be severe enough that you are
unlikely to want to continue processing (such as a memory exceeded error), but
at least you can trap them and exit gracefully.
20–25 Very severe. These are generally system-level errors. Your server-side code will
never know this kind of error happened, as the script and connection will be terminated
immediately.
Keep these in mind — if you need to handle errors outside the 11–19 level range, then you’ll need to
make other plans.
Now, to test this out, we’ll make some alterations to our CREATE script that we built back when we were
looking at IF...ELSE statements. You may recall that part of the reason for our original test to see
whether the table already existed was to avoid creating an error condition that might have caused our
script to fail. That kind of test is the way things have been done historically (and there really wasn’t
much in the way of other options). With the advent of TRY/CATCH blocks, we could just try the CREATE
and then handle the error if one were given:
BEGIN TRY
-- Try and create our table
CREATE TABLE OurIFTest(
Col1 int PRIMARY KEY
);
END TRY
BEGIN CATCH
-- Uh oh, something went wrong, see if it’s something
-- we know what to do with
DECLARE @ErrorNo int,
@Severity tinyint,
@State smallint,
@LineNo int,
@Message nvarchar(4000);
SELECT
@ErrorNo = ERROR_NUMBER(),
@Severity = ERROR_SEVERITY(),
@State = ERROR_STATE(),
@LineNo = ERROR_LINE (),
@Message = ERROR_MESSAGE();