When additional statistics may be useful

To determine when additional statistics are useful, run queries using dbcc traceon(302) and statistics io. If there are significant discrepancies between the “rows to be returned” and I/O estimates displayed by dbcc traceon(302) and the actual I/O displayed by statistics io, examine these queries for places where additional statistics can improve the estimates. Look especially for the use of default density values for search arguments and join columns.

See “Tuning with dbcc traceon(302)” for more information.