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

From: FrankHamersley <FrankHamersleyZat_at_hotmail.com>
Date: Thu, 24 Nov 2005 12:28:46 GMT
Message-ID: <2mihf.2809$ea6.957@news-server.bigpond.net.au>

michael_at_preece.net wrote:
> Hugo Kornelis wrote:

>>On Wed, 23 Nov 2005 01:09:56 GMT, Frank Hamersley wrote:
>>>Hugo Kornelis wrote:
>>>[..]
>>>>Mind you, I don't *KNOW* it can, since I know nothing about Pick. But
>>>>the description of Pick's data structure that DonR wrote (message-ID
>>>><1132350557.673092.92800_at_g49g2000cwa.googlegroups.com>) reminds me very
>>>>strongly of XML. And in XML, it's easy to simply remove a "field" from a
>>>>"row": in "<Person><Name>Hugo Kornelis</Name></Person>", there are no
>>>>tags for birthdate, which clearly indicates that the value for my
>>>>birthdate is absent in this piece of data.
>>>
>>>Is "<Person><Name>Hugo Kornelis</Name></Person>" the same as
>>>"<Person><Name>Hugo Kornelis</Name><Birthday></Birthday></Person>"?
>>
>>Hi Frank,
>>
>>I don't think so.

>
> I agree. They're not the same.
>

>>I the first XML string, there is no Birthday attribute
>>for me. It's missing. In SQL, this would be represented by NULL in the
>>table, or my omitting the row if the birthday were stored in a seperate
>>table.

>
> Omitting the row sounds right. Using NULL is certainly wrong. The thing
> doesn't exist. Nor does <WhatYouDidLastNight/>. Using NULL for
> everything that doesn't exist would take up a considerable amount of
> storage space - like the size of the known universe and more.

Everything after the 1st sentence of the preceding para itself is worthy of NULL. Nuff said!

>>In Pick, this would (as I understand it) be stored by omitting
>>the cell for Birthday.

>
> In the first example, yes.
>

>>The second XML string lists a blank birthday for me. That can't be
>>stored in SQL, as it's strong typing prevents a date from being blank.

>
> It should be represented by NULL. NULL is, after all, regardless of
> data type.
>

>>The Pick data model appears to accept this (unless the DB engine checks
>>before inserting the data), as does XML.

>
> Correct.
>

>>Best, Hugo

>
> Regards
> Mike.

Where it gets more interesting is if you throw the following at the RM (Pick will have no trouble AFAICT).

<People><Person><Name>Hugo Kornelis</Name></Person> <Person><Name>Frank
Hamersley</Name><Birthday>19980706</Birthday></Person></People>

Cheers, Frank. Received on Thu Nov 24 2005 - 06:28:46 CST