SQL Server Execution Plans - Red Gate Software

Chapter 8: Advanced Topics
If you rerun Listing 8.9, you'll see that the execution plan is the same as that shown in
Figure 8.10. However, the query stored in the Select operator is not the same. It now
looks as shown in Listing 8.11.
SELECT 42 AS TheAnswer ,
em.EmailAddress ,
e.BirthDate ,
a.City
FROM Person.Person AS p
JOIN HumanResources.Employee e
ON p.BusinessEntityID = e.BusinessEntityID
JOIN Person.BusinessEntityAddress AS bea
ON p.BusinessEntityID = bea.BusinessEntityID
JOIN Person.Address a ON bea.AddressID = a.AddressID
JOIN Person.StateProvince AS sp
ON a.StateProvinceID = sp.StateProvinceID
JOIN Person.EmailAddress AS em
ON e.BusinessEntityID = em.BusinessEntityID
WHERE em.EmailAddress LIKE 'david%'
AND sp.StateProvinceCode = @0
Listing 8.11
Instead of the two-character string we supplied in the original query definition, the
parameter, @0, is used in the comparison to the StateProvinceCode field. This could
seriously affect performance, either positively or negatively. However, this does increase
the likelihood that, if this query is called again with a different two- or three-character
state code, the plan will be reused.
Before proceeding, be sure to reset the parameterization of the AdventureWorks2008R2
database.
ALTER DATABASE AdventureWorks2008R2
SET PARAMETERIZATION SIMPLE
GO
Listing 8.12
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