Merge pull request #4046 from pmasl/patch-34

PRMerger6 · web-flow · commit 5729e199f611 · 2017-11-21T07:12:04.000Z
Update statistics.md
diff --git a/docs/relational-databases/statistics/statistics.md b/docs/relational-databases/statistics/statistics.md
@@ -73,6 +73,9 @@ For each histogram step above:
 #### Density Vector  
 **Density** is information about the number of duplicates in a given column or combination of columns and it is calculated as 1/(number of distinct values). The query optimizer uses densities to enhance cardinality estimates for queries that return multiple columns from the same table or indexed view. The density vector contains one density for each prefix of columns in the statistics object. 
 
+> [!NOTE]
+> Frequency is information about the occurrence of each distinct value in the first key column of the statistics object, and is calculated as row count * density. A maximum frequency of 1 can be found in columns with unique values.
+
 For example, if a statistics object has the key columns `CustomerId`, `ItemId` and `Price`, density is calculated on each of the following column prefixes.
   
 |Column prefix|Density calculated on|  
