NULL Values In The Histogram

Taiob Ali explains how NULL values show up in the SQL Server histogram when you create statistics:

In the density_vector section ‘All density’ value for column ‘PickingCompletedWhen’ is 0.0004705882 which was calculated from: 1/(Number of distinct values of column ‘PickingCompletedWhen’).
In this case which is 1/2125. All NULL values were considered as one. If you do a count of distinct values you will get a result of 2124. Reason is explained here. If you do a select of all distinct values NULL will show along with other 2124 values.

Taiob explains that there’s really nothing special about NULL when it comes to statistics.

Related Posts

Collecting Statistics Usage Info

Grant Fritchey shows us how (safely) to collect data on statistics usage: Years ago I was of the opinion that it wasn’t really possible to see the statistics used in the generation of a query plan. If you read the comments here, I was corrected of that notion. However, I’ve never been a fan of using […]

Read More

Understanding DBCC SHOW_STATISTICS Outputs

Bill Wolf continues his series on statistics by looking at what DBCC SHOW_STATISTICS gives you: When I was putting together the lesson plans for this, I wanted to make my own query for the comparisons, not borrow one from another site or blog.  Yes, I borrow plenty, but I wanted this to be mine.  When […]

Read More