Re: PostgreSQL Certification

Christopher Browne <cbbrowne@acm.org> writes:

> At one extreme, Chris Date holds to the position that NULLs ought to
> be forbidden outright.  He does make a fairly credible case for it,
> albeit with the problem that when you forbid NULLs, you have to
> replace them by making the data model a little more complex.  (He
> recently released a paper on how to do this; there's not much
> surprise to it; whenever a column "could be NULL," you have to split
> it off to a separate table so that its omission amounts to not
> bothering to populate the new table...)
>
> The other "major" position is that there should be multiple sorts of
> 'NULL' values to indicate different forms of missing information.
> (One problem with NULL is that you can't easily distinguish between
> "I left that NULL because I didn't know the value" and "That's NULL
> because that's how we say it's 'empty.'")
>
> I fall more into the pragmatic position that "NULL columns have the
> potential to cause a lot of confusion; use NOT NULL when you can,
> and be wary when you can't."

Interesting.  The bullet caught my eye because I am currently working
with a table that has, in my opinion, poorly thought out NOT NULL
constraints.  When I do the initial insert I have to use 0 to mean
both "I don't know the value yet" and "this is how we say empty"!  It
occurs to me that adding a cross-reference table would not only let me
avoid NULL, but also solve a couple of other problems as well.

Thanks,
Jon
--
  But if serving the LORD seems undesirable to you, then choose for
  yourselves this day whom you will serve . . . But as for me and my
  household, we will serve the LORD.
  -- Joshua 24:15 (NIV)