Re: So what's null then if it's not nothing?

In message <1132453410.574645.187030_at_f14g2000cwb.googlegroups.com>, JOG <jog_at_cs.nott.ac.uk> writes
>Even hearing the word "null" is starting to sound embarrassing now,
>never mind postulating a definition for it. Surely the field has
>reached the point where we all know there are better ways of handling
>missing data, but given the tech we have when we get up tomorrow, and
>the job at hand, we have to make do. What more is there to say.

Databases and data manipulation techniques evolve. The debate here may influence the future design of those systems.

My contribution to the debate is to point out that the Null value doesn't necessarily indicate missing data. That is one of several different uses of Null. It can also mean Not Applicable, which is not the same thing as Unknown.

I f you want a one sentence description then the best I can come up with is that when a database is interrogated a Null value is equivalent to the politician's favourite answer, "No Comment." You can infer from this that the value is unknown but the reply "Null" doesn't actually tell you that this is so.

Consider the question "When did you stop beating your wife?"

Someone who is unmarried can't respond with a date, even though they know the answer. The correct answer is Null, but this does not mean that the answer is unknown. Any debate that works on the assumption that Null necessarily means unknown is based on a false premise and will possibly produce paradoxical conclusions.

-- 
Bernard Peek
London, UK. DBA, Manager, Trainer & Author.