[Tuning] Filtered indexes...and filtered statistics.

So, SQL Server (starting with 2008) now has Filtered Indexes. Which are great - since an index is basically just a copy of the data, why copy particular fields for the entire table when you only query particular subsets of data? Add a WHERE clause to your index, and now you're querying subsets of data.


However, while reading up on it I came across this:
http://msdn.microsoft.com/en-us/library/ms190397.aspx
which introduces filtered statistics(!).

Instead of

CREATE STATISTICS BikeWeights
    ON Production.Product (Weight)

which would give you stats for the entire range, do this:

CREATE STATISTICS BikeWeights
    ON Production.Product (Weight)
WHERE ProductSubcategoryID IN (1,2,3)

which will only compute statistics for that subset of data.