Special Indexing and Storage Features - Pro SQL Server Internals - page 85

Listing 4-6. Included vs. key columns: Selecting by LastName and FirstName
select CustomerId, LastName, FirstName
from dbo.Customers with (index = IDX_Key)
where LastName = 'Smith' and FirstName = 'Andrew';
select CustomerId, LastName, FirstName
from dbo.Customers with (index = IDX_Include)
where LastName = 'Smith' and FirstName = 'Andrew';
Figure 4-6. Included vs. key columns: Selecting by LastName and FirstName