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From:Gerald Clark Date:April 13 2000 12:54pm
Subject:Re: Two Questions: Adding on a NULL & Multi-table Deletes
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Mark D Wolinski wrote:

> >>- My question is that I defined the column access as INT (which can
> >>- be NULL),
> >>- however, when the statement runs, access isn't updated.  It's not
> >>- necessarily a problem as I can go back and define the necessary columns
> as
> >>- NOT NULL, but is this the proper way the system should handle it.
> >>-  It seems
> >>- to me that if you're adding one (or whatever) to the column if it's
> either
> >>- zero or NULL it should become what I was adding to it.
> >>
> >>Does it update when the value you're adding to is not NULL?
> >>
> >>NULL is just that -- nothing.  It isn't a number, so you can't add to it.
> >>Any operation carried out on a NULL results in a NULL.  If you wanted a
> >>number to represent 'no access yet', that sounds like zero to me.
>
> It does work fine when the column is not null.
>
> While I understand that NULL is not a number, the definition of the column
> as INT defines that column as holding numerical values.  My argument is that
> in a self increment roll, the column should take the value of the increment
> if it is NULL or add it to its previous value if NOT NULL.
>
> The alternative is, if we want the ability to have a NULL column is to first
> check to see if it's null, then if it isn't self increment it, if it is set
> it to the increment already.
>
> I'm not implying that mySQL is broke.  I'm just questioning the logic behind
> the action in this one instance.
>
> My project is still in development so it does me no harm to change my
> columns to NOT NULL.
>

--- snip ---
NULL, for a numeric column, represents an UNKNOWN value.  If you add 1 to an
unknown value,
what is its's value?  It probably is not "1".
It is still UNKNOWN, or NULL.

So, you see, it is not broken.


Thread
bash: mysql: command not foundLars FORNELL12 Apr
Re: bash: mysql: command not foundmysql12 Apr
  • Two Questions: Adding on a NULL & Multi-table DeletesMark D Wolinski12 Apr
    • RE: Two Questions: Adding on a NULL & Multi-table DeletesRobert Goff12 Apr
      • RE: Two Questions: Adding on a NULL & Multi-table DeletesMark D Wolinski13 Apr
        • RAID_CHUNKSPeter13 Apr
          • Re: RAID_CHUNKSEric Thelin13 Apr
        • Re: Two Questions: Adding on a NULL & Multi-table DeletesGerald Clark13 Apr
        • Re: Two Questions: Adding on a NULL & Multi-table DeletesThimble Smith13 Apr
      • Re: Two Questions: Adding on a NULL & Multi-table Deletes(Harald Fuchs)15 Apr
        • RE: Two Questions: Adding on a NULL & Multi-table DeletesMark D Wolinski17 Apr