SQL Server 2008
Filtered statistics are introduced, and these can be created separately from a filtered index. There are some limitations around filtered indexes with regard to the Query Optimizer (see Tim Chapman’s post The Pains of Filtered Indexes and Paul White’s post Optimizer Limitations with Filtered Indexes) post, and it’s important to understand the behavior of the counter that tracks modifications (and thus can trigger automatic updates). See Kimberly’s post Filtered indexes and filtered stats might become seriously out-of-date for more details, and I also recommend checking out her stored procedure that analyzes data skew and recommends where you can create filtered statistics to provide more information to the Query Optimizer. I’ve implemented this for several large customers that have VLTs and skewed distribution across columns frequently used in predicates.
Two new catalog views, sys.stats and sys.stats_columns, are added to provide easier insight into statistics and included columns. Use these two views instead of sp_helpstats, which is deprecated and provides less information.
This is a very interesting historical look. Most interesting to me was the decreases in the number of steps available.