Sql updating statistics

To view this histogram, go to the details tab of the statistic’s properties or use the command DBCC SHOW_STATISTICS.The screenshot below shows the histogram of an index statistic; the RANGE_HI_KEY is the upper limit of the step, the RANGE_HI_KEY of the previous step 1 is the lower limit, and the RANGE_ROWS is the count of rows between the limits.

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If you omit the WHERE clause, all records in the table will be updated!

The WHERE clause specifies which record(s) that should be updated.

-Table had less than 500 rows and there is an increase of 500 rows or more since the last update -Table has over 500 rows and there is an increase of 500 20% of the table size since the last update Maintenance plan: You can also proactively update the statistics yourself using TSQL (sp_updatestats for all stats in a database or UPDATE STATISTICS for a single one) or a maintenance plan task.

Scheduling the statistics maintenance during off hours will help reduce the need to update statistics during peak times.

The distribution is a representation of the data contained in the first column of the statistic.

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.A table could end up having a large number of statistics that serve no purpose.It is wise to review and clean up the statistics as part of general maintenance.Statistics contain two different types of information about the data; density and distribution.Density is simply the inverse of the count of distinct values for the column or columns.Column statistics: Created manually by the DBA using the ‘CREATE STATISTICS’ command, or automatically if the “Auto Create Statistics” option is set to “True”.

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