Re: C# Nullable types

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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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