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

The WAITFOR statement does exactly what it says it does — that is, it waits for whatever you specify as
the argument to occur. You can specify either an explicit time of day for something to happen, or you can
specify an amount of time to wait before doing something.
The DELAY Parameter
The DELAY parameter choice specifies an amount of time to wait. You cannot specify a number of days —
just time in hours, minutes, and seconds. The maximum allowed delay is 24 hours. So, for example:
WAITFOR DELAY ‘01:00’;
would run any code prior to the WAITFOR, then reach the WAITFOR statement, and stop for one hour,
after which execution of the code would continue with whatever the next statement was.
The TIME Parameter
The TIME parameter choice specifies to wait until a specific time of day. Again, we cannot specify any
kind of date — just the time of day using a 24-hour clock. Once more, this gives us a one-day time limit
for the maximum amount of delay. For example:
WAITFOR TIME ‘01:00’;
would run any code prior to the WAITFOR, then reach the WAITFOR statement, and stop until 1 AM, after
which execution of the code would continue with whatever the next statement was after the WAITFOR.
TRY/CATCH Blocks
In days of yore (meaning anything before SQL Server 2005), our error-handling options were pretty limited.
We could check for error conditions, but we had to do so proactively. Indeed, in some cases we could
have errors that would cause us to leave our procedure or script without an opportunity to trap it at all
(this can still happen, but we have options that really cut down the instances where it does). We’re going
to save a more full discussion of error handling for our stored procedures discussion in Chapter 12, but
we’ll touch on the fundamentals of the new TRY/CATCH blocks here.
A TRY/CATCH block in SQL Server works remarkably similarly to those used in any C-derived language
(C, C++, C#, Delphi, and a host of others). The syntax looks like this:
BEGIN TRY
{ }
END TRY
BEGIN CATCH
{ }
END CATCH [ ; ]
Chapter 11: Writing Scripts and Batches
In short, SQL Server will “try” to run anything within the BEGIN...END that goes with your TRY block.
If, and only if, you have an error condition that has an error level of 11–19 occurs, then SQL Server will
361