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

Chapter 11: Writing Scripts and Batches
coming up with the same results. The advantage of this is usually more readable code. It is simply easier
to handle a looping structure (or any structure for that matter) if you have a single point of entry and a
single exit. Using a BREAK violates this notion.
All that being said, sometimes you can actually make things worse by reformatting the code to avoid a
BREAK. In addition, I’ve seen people write much slower code for the sake of not using a BREAK statement
— bad idea.
The CONTINUE statement is something of the complete opposite of a BREAK statement. In short, it tells
the WHILE loop to go back to the beginning. Regardless of where you are in the loop, you immediately
go back to the top and re-evaluate the expression (exiting if the expression is no longer TRUE).
We’ll go ahead and do something of a short example here just to get our feet wet. As I mentioned before,
WHILE loops tend to be rare in non-cursor situations, so forgive me if this example seems lame.
What we’re going to do is create something of a monitoring process using our WHILE loop and a WAIT-
FOR command (we’ll look at the specifics of WAITFOR in our next section). We’re going to be automatically
updating our statistics once per day:
WHILE 1 = 1
BEGIN
WAITFOR TIME ‘01:00’;
EXEC sp_updatestats;
RAISERROR(‘Statistics Updated for Database’, 1, 1) WITH LOG;
END
This would update the statistics for every table in our database every night at 1 AM and write a log
entry of that fact to both the SQL Server log and the Windows application log. If you want check to see if
this works, leave this running all night and then check your logs in the morning.
Note that an infinite loop like this isn’t the way that you would normally want to schedule a task. If you
want something to run every day, set up a job using the Management Studio. In addition to not keeping
a connection open all the time (which the preceding example would do), you also get the capability to
make follow up actions dependent on the success or failure of your script. Also, you can e-mail or netsend
messages regarding the completion status.
The WAITFOR Statement
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There are often things that you either don’t want to or simply can’t have happen right this moment, but
you also don’t want to have to hang around waiting for the right time to execute something.
No problem — use the WAITFOR statement and have SQL Server wait for you. The syntax is incredibly simple:
WAITFOR
DELAY | TIME