Erik Darling tells the unpleasant truth about NULL:
Table definitions have a similar effect on developers. In today’s post, I’m going to use temp tables as an example, but the same thing can happen with regular tables, too.
The issue isn’t with NULL values themselves, of course. The table definition we’re going to use will allow NULLs, but no NULLs will be present in the data.
The issue is with how you query NULLable columns, even when no NULLs are present.
As a card-carrying member of the League of No-Null Workers, I am happy to tell you all about how much I hate NULL in databases. And this isn’t even the big reason.