Implement Default SQL logic

[migaman]

Specify ISO compliant behavior of the Equals (=) and Not Equal To (<>) comparison operators when they are used with null values.
All comparisons against a null value evaluate to UNKNOWN.

Skyline behaviour.

• Rows containing NULL values (in relevant Skyline attributes) are always in the Skyline.

Sorting Behaviour

• NULL values result as TOP result during sorting

[migaman]

See also option SET ANSI_NULLS

In a future version of SQL Server, ANSI_NULLS will always be ON and any applications that explicitly set the option to OFF will generate an error. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.
[(https://msdn.microsoft.com/en-us/library/ms188048.aspx)]