Statistics are made up of three parts. Each part tells the optimizer important information regarding the make up the table’s data distribution.
Header – Last Time Stats were updated and number of sample rows
Density Vector – Uniqueness of the columns or set of columns
Histogram– Data’s distribution and frequency of distinct values
Let’s look at a Header, Density and Histogram example.
You can read what the statistic are broken down into using DBCC SHOW_STATISTICS. All field definitions are taken from MSDN.
This is from AdventureWorks2016CTP3 sample database, if you want to follow along. Using the Sales. SalesOrderDetail table let’s look the stats and see what we can find out what it shows us.
Read the whole thing.