In this fourth and final part in my series about NULL, I’ll discuss some well-known and some less well-known functions and keywords that are specifically created to deal with NULL values. And I will, of course, explain why null if null is null null null is null. In case you have not yet read them, you can click these links to read the first, ...

Two months ago, I posted the first two parts of a series about NULL. After that, I went quiet. Much to do and little time was one excuse. But to be honest, I also lost interest. However, I felt I owe my readers to conclude the series, so I have now forced myself to write and publish the last parts before moving on to more interesting subjects ...

In my previous post, I explained what NULL does and does not mean, how and why the rule of NULL propagation forces any expression involving NULL to result in NULL. I also mentioned that comparisons involving NULL do not result in NULL but, rather, in a new “truth value” called “Unknown”. But there’s a lot more to be written about Unknown and it’s ...

I once read a scientific article on black holes that started of on the observation that, since a hole is the absence of anything and black is invisible in space, a black hole is in fact an invisible nothing – so what the heck are we talking about? Well, almost the same can be said about NULL in databases.   Let’s first take a look at what ...