I hope you have found my blog series about NULLs useful. I was inspired to write this series by Jeff Davis’s 2009
blog entry on the topic, in which he states:

“Oh, that makes sense” — When you see individual behaviors of NULL, they look systematic, and your brain quickly
sees a pattern and extrapolates what might happen in other situations. Often, that extrapolation is wrong, because NULL semantics
are a mix of behaviors. I think the best way to think about NULL is as a Frankenstein monster of several philosophies and systems
stitched together by a series of special cases.

The Wikipedia article about NULLs is quite thorough, including
criticisms. This C. J. Date
book excerpt also has a good summary of possible
NULL traps to avoid.

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