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If a plan does not exist in cache for a query, then if the optimizer uses a statistics object that is out of date when the plan compiles, SQL Server will automatically update those statistics.
Now let’s issue an update against statistic object automatically updated.
We could simply assume that the optimizer used this object in the plan.
The technical article, Statistics Used by the Query Optimizer in Microsoft SQL Server 2008, documents these thresholds.
For a regular table, statistics are out of date when:o The table had more than 500 rows when the statistics were gathered, and the colmodctr of the leading column of the statistics object has changed by more than 500 20% of the number of rows in the table when the statistics were gathered (test 3). Sales Order Detail table has 121317 rows:(121317 * 0.20) 500 = 24764The bulk insert below loads 24775 rows, which should be enough to invalidate statistics. The statistics have not updated, but the modification counter has changed, as expected.
Summary As I stated initially, I wanted to write this post to clear up any confusion surrounding automatic updates for statistics.