2 August 2009
Jeff Davis has written a superb article about the problems with NULL in SQL. He has it exactly right when he says:
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 closest single operational definition of
NULL I can think of is, “This could be any value, so I-the-database will not treat it as being any particular value.” Of course, that immediately breaks given that aggregates ignore nulls.
This is, sadly, one of those things that you just have to learn. Painfully.