Nice work Leo, good article on indexes, but should also include a general definition of what a clustered vs non-clustered, but this may be in the book. Also, indexes will change over time since how data is acessed will change, queries change as the database and apps over the db update as business domain rules change. Bottom line is to use indexes when necesary to minimixe table scans, and remove them when no longer needed.

Simple/general definition of cluster and non_cluster.

cluster: like the table of contents of a book in some common grouping.

non cluster: like the index in the back ordered in some general order.

Cheers!