Note: To demonstrate the correctness and stability due to a sound theoretical foundation relative to the industry's fad-driven "cookbook" practices, I am re-publishing as "Oldies But Goodies" material from the old DBDebunk.com (2000-06), so that you can judge for yourself how well my arguments hold up and whether the industry has progressed beyond the misconceptions those arguments were intended to dispel. I may revise, break into parts, and/or add comments and/or references.
In response to a LinkedIn thread where interest was expressed in a "NULL research" project, we re-publish as "Oldies But Goodies" a series of old exchanges with readers reacting to our The Final NULL in the Coffin: A Relational Solution to Missing Data: in Parts 1, 2, 3 we re-published a past exchange between myself and Hugh Darwen with a reader on the pros and cons of our solution vs. Hugh Darwen's "horizontal decomposition" NULLless solution, and in Part 4 my debunking of reactions to an article of mine on the subject which exhibit the confusion inevitably evoked by NULL.
We complete this series with an exchange with a reader who claimed that our criticism applies to SQL's specific implementations of NULL, not to the NULL concept itself. I and David McGoveran explained that the implementation flaws in SQL derive directly from the deeper problems endemic to many-valued logics.