Special Indexing and Storage Features
This chapter discusses several storage- and indexing-related features available in SQL Server. It covers indexes with included columns, filtered indexes and statistics, data compression, and sparse columns.
Indexes with Included Columns
As you already know, SQL Server rarely uses nonclustered indexes when it expects that a large number of Key or RID Lookups is required. Those operations usually lead to a large number of reads, both logical and physical.
With Key Lookup operations, SQL Server accesses multiple data pages from different levels in a clustered index every time it needs to obtain a single ...