13.5. Managing statistics
Earlier in the chapter we looked at the important role played by statistics in providing the query optimizer with information on the selectivity of an index and the likely value it therefore has for use in a given query. In addition to maintaining statistics on index selectivity, statistics are created and maintained for nonindexed columns as well. In this section we'll take a further look at index statistics and introduce column statistics.
13.5.1. Index statistics
The default statistics configuration enables SQL Server to automatically create and update statistics on all indexed columns. This setting reduces maintenance requirements and ensures SQL Server makes accurate decisions when creating query execution plans. ...