Re: 3vl 2vl and NULL

Hugo Kornelis wrote:

> On 4 Dec 2005 17:57:01 -0800, michael_at_preece.net wrote:
>
> (snip)
> >OK. There is one fundamental problem with this. Some of those NULLs in
> >those tuples might represent that we know something is empty - so it
> >has to be treated as a known value. All NULLs are not created equal.
>
> <sigh>
>
> Hi Mike,
>
> No. If something is known to be empty, it's not stored as NULL. At least
> not in SQL databases (which this thread is about, IIRC).
>
> If a comment is empty, iut's stored as the empty string (''). If a
> container is empty, it's contents is stored as zero gallons (0). Dates
> can't be empty. (Days can be, though - that's stored as an absence of
> rows in the Events table).
>
> Best, Hugo

What type of liquid is stored in an empty mug? Is it "unknown"? No - it is not an unknown type of liquid. It is no liquid. The value of the "liquid" column for the row would be empty. It would be NULL.

Super,
Mike. Received on Tue Dec 06 2005 - 03:17:49 CET