Articles Posted in the " histogram " Category

  • NULL Values in Histogram

    During my cardinality estimator presentation in DBA virtual group there was a question asked about NULL values and histogram. I am quoting the question as is “SQL Server include null values in the index. How are statistics handle for null values?”

    I will answer the question in this blog post.

    For demo purpose I will be using WideWorldImporters database which you can download and restore from here. In table [Sales].[Orders] column ‘PickingCompletedWhen’ does allow NULL values.

    How many rows are NULL and how many are NOT NULL?

    USE [WideWorldImporters];
    GO
    SELECT 'NULL' AS [Value], COUNT(*) AS [NumOfRecord]
    FROM [Sales].[Orders]