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 I was presenting my “code tuning” class, I had recently upgraded my instance from 2012 to 2017.  I had also put my database into 2017 compatibility mode.  I had used this query to show that unions that are intensive can cause issues with tempdb and cause spill over.  To my “joy”, when I ran the query in the class I did not get the tempdb spillover.  And right then I realized that I was not in Kansas(2012 compatibility) any longer.  But this proved to be opportunistic for the statistics/optimizer comparison.

Read on for a discussion of the cardinality estimator as well.

Related Posts

The Importance of Cardinality

Bert Wagner shows us why cardinality is important to understand when indexing data: When building indexes for your queries, the order of your index key columns matters.  SQL Server can make the most effective use of an index if the data in that index is stored in the same order as what your query requires for […]

Read More

Calculating Skew In SQL

Lukas Eder shows how you can use PERCENTILE_DISC to calculate skewness in SQL: In RDBMS, we sometimes use the term skew colloquially to mean the same thing as non-uniform distribution, i.e. a normal distribution would also be skewed. We simply mean that some values appear more often than others. Thus, I will put the term […]

Read More

Categories

January 2018
MTWTFSS
« Dec Feb »
1234567
891011121314
15161718192021
22232425262728
293031