Re: So what's null then if it's not nothing?
Date: Tue, 29 Nov 2005 13:21:12 GMT
David Cressey wrote:
> "Frank Hamersley" <terabitemightbe_at_bigpond.com> wrote in message
>>It has always escaped me why Sybase particularly (and perhaps others) >>convert '' to ' ' for varchar attributes. I must admit I haven't >>applied much brain power to rationalising the impact on the query engine >>of unwinding this behaviour, but on first impression can't understand >>why NULL, '' and ' ' are not distinguishable. Curiously RTRIM('') gives >>NULL as a result! >> >>Anyway, thats the way it is. Perhaps someone can turn on the light?
> The engineers are not infinite in their wisdom.
> The most robust solution for storing NULLS is a bit vector stored with each
> row, that indicates whether data is present or not present in each of the
> cells. However, this adds overhead. DEC Rdb did it this way. DEC's
> solution has the overhead, even in cases where a coulmn is declared NOT
> Oracle chose to indicate a null by the "impossible values" method. For
> example, A NULL in a NUMBER is represented by minus zero. A single zero
> byte is used to represent a NULL in a VARCHAR. Unfortunately, an empty
> string, having length zero, gets the same representation. Oops!
> I don't know about Sybase.
On zip research I am guessing the "impossible values" method given their propensity to force '' to ' ' to avoid embarassment and confusion.
Cheers, Frank. Received on Tue Nov 29 2005 - 14:21:12 CET