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

Chapter 10: Views
You can get the yellow popup by hovering your mouse over the top-left node of the execution plan. This
is the top node of the execution plan, and looking at the Estimated Subtree Cost on this node shows us
the estimated coast for the entire query (for me, it is 3.49114). Now that we’ve seen how complex the
query is and seen the estimated cost, we’re ready to move on to creating the index.
When we create the index, the first index created on the view must be both clustered and unique:
CREATE UNIQUE CLUSTERED INDEX ivCustomerOrders
ON CustomerOrders_vw(AccountNumber, SalesOrderID, ProductID);
Once this command has executed, we have a clustered index on our view (Figure 10-6), and we’re ready
to again check out our Estimated Execution Plan for our basic SELECT.
Figure 10-6
Notice that this is a substantially more simplistic query. The estimated cost of execution has also
dropped by over 50%. Does this mean our index is a good idea? Well, simply put — no. It means it might
be. Much like any index, you need to keep in mind the maintenance cost of the index. How much is
maintaining this index going to slow down INSERT, UPDATE, and DELETE statements against the underlying
tables? Basically, it’s a balancing act, and each database and each index is a separate decision. That
said, indexed views can be a powerful tool to have in your arsenal, so weigh them carefully!
Summary
322
Views tend to be either the most over- or most under-used tools in most of the databases I’ve seen. Some
people like to use them to abstract seemingly everything (often forgetting that they are adding another
layer to the process when they do this). Others just seem to forget that views are even an option. Personally,
like most things, I think you should use a view when it’s the right tool to use — not before, not after.
Things to remember with views include:
❑ Stay away from building views based on views — instead, adapt the appropriate query information
from the first view into your new view.
❑ Remember that a view using the WITH CHECK OPTION provides some flexibility that can’t be
duplicated with a normal CHECK constraint.