Sql server statistics not updating
Column statistics can be created, modified and dropped at will.
Statistics contain two different types of information about the data; density and distribution.
These will have the same name as the index and will exist as long as the index exists.
Column statistics: Created manually by the DBA using the ‘CREATE STATISTICS’ command, or automatically if the “Auto Create Statistics” option is set to “True”.
Brent Ozar believes that this should be done much more regularly then doing reorgs or rebuilds on indexes.
By updating your statistics SQL Server is more likely to create a 'better' query plan.
Scheduling the statistics maintenance during off hours will help reduce the need to update statistics during peak times.
The update occurs before executing a query if certain conditions are met, or after the query is executed if Auto Update Statistics Asynchronously is used instead.This information is stored in a histogram; the histogram contains up to 200 steps with a lower and upper limit and contains the count of values that fall between both limits.To view this histogram, go to the details tab of the statistic’s properties or use the command DBCC SHOW_STATISTICS.When examining a query execution plan, a large discrepancy between the Actual Number of Rows and the Estimated Number of Rows is an indication of outdated stats.Outdated statistics can lead the optimizer in choosing inefficient execution plan and can dramatically affect overall performance.