Re: C# Nullable types

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I will just end with how the SQL Server doc explains this.

http://msdn2.microsoft.com/en-us/library/ms191504.aspx :
"Null values generally indicate data that is unknown, not applicable, or
that the data will be added later."

I'm not sure what is the point you don't like in this definition that looks
quite close to mine but it really looks like that understanding each other
on this topic is out of reach.

Take care and see you soon in another thread for another heated discussion
;-)

--
Patrice

"Scott M." <s-mar@xxxxxxxxxxxxx> a écrit dans le message de news:
OMPOZW5dHHA.4308@xxxxxxxxxxxxxxxxxxxxxxx
I think you are making my point here. You introduced the concepts and
terms: "unknown", "undefined" and "not applicable" into the disussion. In
addition, you are talking about "why" a database needs the concept of a
null (I personally think you mis-stated that, but that is besides the
point).

Below, you are talking about the practical use of null, rather than the
meaning of null, which is the point of this thread.


"Patrice" <http://www.chez.com/scribe/> wrote in message
news:ecXux94dHHA.4032@xxxxxxxxxxxxxxxxxxxxxxx
I'm not using null when "I don't know what value the user may want to
input" (actually I never know what value the user will enter, not sure
what you meant).

Also I don't use NULL when "I'm letting the user not put any value at all
into the field" which is IMO bad form at least to do systematically. I'll
use an empty string or 0 as a default value if it makes senses.

I will use this for example for the actual start date of something that
not started yet. In this case you can't provide any value. IMO this is a
more convincing sample than Appartement number and the like where in a
real world scenario you never want to distinguish between a value that
can't be provided for some reason (null) and the fact that the apartment
number is just an empty string because you *know* this is an empty
string, not because you are unable to provide this value.

This is perhaps why I tried at first to explain what's behind null. I
felt that using simply the word "null" was perhaps not sufficient as it
is IMO sometimes misused.

---
Patrice

"Scott M." <s-mar@xxxxxxxxxxxxx> a écrit dans le message de news:
OTi6AT4dHHA.1244@xxxxxxxxxxxxxxxxxxxxxxx
Hmmm, again, to my knowledge the concepts of "undefined", "unknown","
not applicable" have never been identified with "null" in SQL or
anywhere else. When I mark a filed in SQL as "nullable", I am not doing
it because I don't know what value the user may want to put into the
field. On the contrary, I do it because I'm letting the user not put
any value at all into the field.

Again "undefined", "unknown"," not applicable" does not equal "null". I
think this is super-important to be clear on, because "null" has a
special purpose and meaning and the minute you try to attach a meaning
that is something similiar, but not the same, to it, you confuse the
issue and make it more complicated than it need be.


"Patrice" <http://www.chez.com/scribe/> wrote in message
news:%23wpuDg1dHHA.1868@xxxxxxxxxxxxxxxxxxxxxxx
OK I perhaps see a bit better your semantic point. AFAIK some
additional "markers" were suggested in SQL standards to better define
various meanings of "undefined", "unknown"," not applicable" or several
other semantics given to NULL values but never made into products...

I perhaps miss also some nuances as English is not my native language
but hopefull the overall picture should be clear enough for the OP.


"Scott M." <s-mar@xxxxxxxxxxxxx> a écrit dans le message de news:
ulQ8h4udHHA.284@xxxxxxxxxxxxxxxxxxxxxxx
Something having an unknown value is not, in any way, related to a
dissussion of null. The very word you use "unkown" implies that there
is, in fact, something to "know". A null value indicates the exact
opposite of that, that there is no value at all. That's why I said
that your alaogy was not a good one.

When I run into situations where a value is unknown to me, I set up a
variable to capture that value. After doing that, I can then look to
see if the varialbe is null, seven, "green" or anything else. The
fact that I didn't know the value of the variable does not imply null.

You seem to be discussing what a "nullable type" is, rather than the
meaning of "null".




"Patrice" <http://www.chez.com/scribe/> wrote in message
news:esbV%23RudHHA.4188@xxxxxxxxxxxxxxxxxxxxxxx
Not sure what you meant. How would you mark that the price is unknown
if not using a "nullable" type representing a null value ? As a side
note, an empty string is not a "null" string (in the first case we
known that the value is a zero length string, in the other case we
don't know what the value is).

IMO one of the problem in discussing is that null has multiple
acceptances. In the context of a nullable type this is the same than
the "NULL" (Il'l use uppercase for this meaning) marker used in most
DB, not the "null" refererence as usual in C# (likely why MS used
HasValue for what is called "nullable" types toa void the ambiguity).
VB.NET uses the Nothing keyword.

Finally I see sometimes what is IMO an abusive use of NULL. If you
know that you have no name suffix, you don't have to use a NULL value
but an empty string will do. You have to use a NULLable column if you
want to distinguish if the value is an empty string or if it has no
meaning (i.e. not "known", "applicable" or whatever semantic you
attribute to the NULL value).
---
Patrice


"Scott M." <s-mar@xxxxxxxxxxxxx> a écrit dans le message de news:
%23NBysutdHHA.4636@xxxxxxxxxxxxxxxxxxxxxxx
I would have to disagree with your analogy.

If someting is free, it still has a value of zero dollars (as you
say), but if we don't know the price, that doesn't make the price
null, it just makes the price unkown.

null is simply a keyword that indicates that the item in question
does not have a relationship to any data at all.

A = 0 <-- A has a value of zero
A = " " <-- A has a value of the space char
A = "" <-- A has a null value (no data at all)

The benefit of null values is primarially when using databases,
since most databases have tables where not all fields are required
to have a value (like a middle name or apartment number or name
suffix, such as Sr. or Jr.). Since it is possible that a field may
be null, we need a way of checking it as such or passing null values
into it.

-Scott

"Patrice" <http://www.chez.com/scribe/> wrote in message
news:uiUEhoqdHHA.1220@xxxxxxxxxxxxxxxxxxxxxxx
For example for a price it would allow to distingusih between
something that is free (0) and something for which don't know the
price (null).

It's likely you'll mostly use this for dates (if the vetn occured
the date will be filled, if the event didnt' occured date, the date
will be null).

---
Patrice

"AVL" <AVL@xxxxxxxxxxxxxxxxxxxxxxxxx> a écrit dans le message de
news: 49380D43-FF22-4652-98B0-82E7C30DEC82@xxxxxxxxxxxxxxxx
hi,
i'm a new bie to c#.net 2.0....
i've come across a new feature by name nullable types...need some
info on it

what is actually a null value...
what exactly is advantage we get by specifying a value type as a
null value...

please clarify


















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