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

DECLARE @RowCount int; --Notice the single @ sign
SELECT * FROM Person.Person;
SELECT @RowCount = @@ROWCOUNT;
This again shows us all the rows, but notice the new line that we got back:
The value of @@ROWCOUNT was 19972
We’ll take a look at ways this might be useful when we look at stored procedures later in the book. For
now, just realize that this provides us with a way to learn something about what a statement did, and it’s
not limited to use SELECT statements — UPDATE, INSERT, and DELETE also set this value.
Batches
If you look through the example, you might notice that, much as I did with @@IDENTITY,
I chose to move the value off to a holding variable. @@ROWCOUNT will be reset with a
new value the very next statement, so, if you’re going to be doing multiple activities
with the @@ROWCOUNT value, you should move it into a safe keeping area.
A batch is a grouping of T-SQL statements into one logical unit. All of the statements within a batch are
combined into one execution plan, so all statements are parsed together and must pass a validation of
the syntax or none of the statements will execute. Note, however, that this does not prevent runtime errors
from happening. In the event of a runtime error, any statement that has been executed prior to the runtime
error will still be in effect. To summarize, if a statement fails at parse-time, then nothing runs. If a statement
fails at runtime, then all statements until the statement that generated the error have already run.
All the scripts we have run up to this point are made up of one batch each. Even the script we’ve been
analyzing so far this in chapter makes up just one batch. To separate a script into multiple batches, we
make use of the GO statement. The GO statement:
❑ Must be on its own line (nothing other than a comment can be on the same line); there is an
exception to this discussed shortly, but think of a GO as needing to be on a line to itself.
❑ Causes all statements since the beginning of the script or the last GO statement (whichever is closer)
to be compiled into one execution plan and sent to the server independently of any other batches.
❑ Is not a T-SQL command, but, rather, a command recognized by the various SQL Server command
utilities (sqlcmd and the Query window in the Management Studio).
A Line to Itself
The GO command should stand alone on its own line. Technically, you can start a new batch on the same
line after the GO command, but you’ll find this puts a serious damper on readability. T-SQL statements
cannot precede the GO statement, or the GO statement will often be misinterpreted and cause either a
parsing error or some other unexpected result. For example, if I use a GO statement after a WHERE clause:
SELECT * FROM Person.Person WHERE ContactID = 1 GO
Chapter 11: Writing Scripts and Batches
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