Steve Jones - Editor (8/18/2010)
NULL seems like a variable to me, in an equation that can't be currently solved. Or maybe like "i". We know that it has some value, but we cannot pick a value to state, so we use a placeholder.
I like this thought Steve, but I would also add that a NULL can represent an "N/A." For instance, if we have a table listing car models, then we might have a column for MPG. But what if the model is an electric car? What would we put in the column for MPG? Would it be wrong to use a NULL there since there really is no quantity that applies? We can't use "N/A" since it is a numeric field.
The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge. - Stephen Hawking