Grant, I confused for a question when I'm reading <Dissecting SQL Server

Execution Plans>:

Following two T-SQL generate two different plans, but I don't know why:

--Clustered index scan

SELECT ContactID,LastName,EmailAddress FROM person.Contact WHERE EmailAddress LIKE 'sa%'

--NonClustered index seek and Key Lookup

SELECT ContactID,LastName,EmailAddress FROM person.Contact WHERE EmailAddress LIKE 'sab%'

Would you give me some suggestion please?

Thanks a lot.

s.pig.snow@gmail.com