“Efficiency is doing things right; effectiveness is doing the right things.”

Peter Drucker

First, a Quick Refresher: “Normal” Indexes

When storing and retrieving data in MS SQL Server, you have two options: Clustered and Nonclustered indexes. A clustered index is your table in a specific order (Think of the old-timey phonebooks). A nonclustered index is typically a smaller subset of fields of the entire table, usually ordered on a different field than your clustered index (Think the index in the back of a textbook). However, both indexes, by default, consist of one record for each row in your table.