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

command-line scripting. By default, these special script commands are not available in the Query window.
Turning sqlcmd mode on activates the special sqlcmd scripting options even in the Query window.
Show Execution Plan
Every time you run a query, SQL Server parses your query into its component parts and then sends it to
the query optimizer. The query optimizer is the part of SQL Server that figures out the best way to run
your query to balance fast results with minimum impact to other users. When you use the Show Estimated
Execution Plan option, you receive a graphical representation and additional information about how
SQL Server plans to run your query. Similarly, you can turn on the Include Actual Execution Plan option.
Most of the time, this will be the same as the estimated execution plan, but you will occasionally see
differences here due to changes that the optimizer decides to make while running the query, as well as
changes in the actual cost of running the query versus what the optimizer thinks is going to happen.
Let’s see what a query plan looks like in our simple query. Click the Include Actual Execution Plan
option, and execute the query again, as shown in Figure 2-13.
Figure 2-13
Chapter 2: Tools of the Trade
Be aware that the Query window always utilizes the SQLNativeClient connection
method (even when operating in sqlcmd mode), whereas the actual sqlcmd utility
will use an OLE DB connection. The result is that you may see slight differences
in behavior between running a script using sqlcmd versus using sqlcmd from the
Query window. These tend to be corner case differences, and are rarely seen and
generally innocuous.
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