Index fragmentation is a phenomenon where the index contents are scattered. Normally the contents are in contiguous fashion which helps in fast retrieval of the underlying data. When the indexes are fragmented the data access becomes time consuming because of the scattered data that needs to be searched and read.
I have used the Contact table with person schema which is residing in AdventureWorks database for testing the index usage. I am describing the scenarios and places where index seek or scan will be used.
Included column is a new feature in SQL Server 2005. When you add a column as an Included column, it gets stored at the leaf level of the index and it is not part of the index key. This only works for non-clustered indexes.