Re: So what's null then if it's not nothing?
Date: 19 Nov 2005 10:16:26 -0800
Marshall Spight wrote:
> michael_at_preece.net wrote:
> > Poor deluded fools. The sooner SQL-relational is seen for what it is -
> > ridiculous - the better.
> I remember you from some previous conversations, and I have
> to say my impression of you is that you're a better person than
> would write this sort of thing. What's going on?
> As to the specific issue at hand, I want to assert in the strongest
> possible terms that the issue isn't about what NULL "is" or isn't.
> We may define our formal systems to have whatever semantics
> we wish. We may come up with better or worse abstractions,
> but whatever we do, it won't be a perfect reflection of the
> "Real World(tm)" so we should drop the whole "is" business and
> simply talk about what's useful.
> Having some kind of representation for missing values is
> not a requirement for a data model, but many people happen
> to find it useful. Having a representation for an unknown
> value is not a requirement for a data model, and I have
> heard almost no one argue that it is a useful thing to have.
> My thinking is that a good design would include a principled
> way of handling missing values, and would exclude any
> special handling of unknown values.
> The question also arises as to what exactly SQL's null "is."
> Is it unknown or empty? The answer, alas, is that it depends
> on the context, a disastrously bad state of affairs. If you have
> a table with a nullable int column and two rows, one null, and
> you select sum(column) from table, you'll see that the nulls are
> treated as empty. If you have a row with two int columns, one
> null, and you select column1 + column2, you'll see that null
> is treated as unknown. This is simply bad design, and not
> any kind of indictment of relational theory.
> As far as my take on "SQL vs. PICK", it seems about as
> likely to provoke rational debate as the Cal vs. Stanford
> football game, (a notorious local long-running rivalry.)
> I'm sick of the whole "vs." part. What I find interesting is
> asking, what did SQL get right, and what did it get wrong?
> I am also interested to consider what Pick got right and
> what it got wrong. Lots of interesting meat for discussion
> there, and perhaps not quite so confrontational.
Received on Sat Nov 19 2005 - 19:16:26 CET