NULL values are excluded. Why?

Question

This is about a bizarre behaviour I found in Microsoft Sql Server. Please correct me if I\'m wrong.

SELECT COUNT(*) FROM TABLEA 
WHERE [Column1] IS NULL;
         


        

Answer 1

This is actually a common mistake made with SQL Server in treating NULL as a value. By default, it's treated as UNKNOWN, as documented here. So, in your view, you also need to include an OR t1.[Column1] IS NULL.

You can change this behavior by calling SET ANSI_NULLS OFF. It is not recommended to use this, however, as the feature is deprecated as pointed out by @Martin Smith.

This is not a SQL Server specific issue, however. It's part of the ANSI SQL standard.