In PHP there is a function named isset - I think there's no shorter version than this.
For context, null is a concept in computer science used to represent the absence of information. Since the 0s and 1s in transistors determine the information in computers, a file where the binary in transistors reads as 00000000000 etc., it would be considered "null" since it would be indistinguishable from a bunch of unpowered transistors.
So like, if I were to "subtract" from a null file, thus causing something similar to integer overflow, what would this "anti-null" file be known as in computer science?
No, there's no "universal acceptor" value in SQL that is equal to everything.
What you can do is raise the NVL into your comparison. Like if you're trying to do a JOIN:
SELECT ...
FROM my_table AS m
JOIN other_table AS o ON o.name = NVL(m.name, o.name)
So if m.name is NULL, then the join will compare o.name to o.name, which is of course always true.
For other uses of NULL, you might have to use another technique that suits the situation.
Adressing the question in the comment on Bill Karwin's answer:
I want to output a 1 if the NEW and OLD value differ and a 0 if they are the same. But (for my purposes) I want to also return 0 for two NULLS.
select
Case When (:New = :Old) or
(:New is NULL and :Old is NULL) then 0
Else
1
End
from dual
Following a common pattern in mathematical language, "co-null" is a reasonable term.
I've seen both "co-null set" and "(set of) full measure" used here. Note that these are each a bit better than "measure $1$," since the latter doesn't mean what it should when the measure of the whole space isn't $1$ (consider the Lebesgue measure on $\mathbb{R}$ as opposed to just $[0,1]$ or similar).
I like the term "full set," but I've never heard it used.
There's the null-safe dereferencing operator (?.) in Groovy... I think that's what you're after.
(It's also called the safe navigation operator.)
For example:
homePostcode = person?.homeAddress?.postcode
This will give null if person, person.homeAddress or person.homeAddress.postcode is null.
(This is now available in C# 6.0 but not in earlier versions)
UPDATE: The requested feature was added to C# 6.0. The original answer from 2010 below should be considered of historical interest only.
We considered adding ?. to C# 4. It didn't make the cut; it's a "nice to have" feature, not a "gotta have" feature. We'll consider it again for hypothetical future versions of the language, but I wouldn't hold my breath waiting if I were you. It's not likely to get any more crucial as time goes on. :-)
To explain to a boss the difference between "zero" and "null":
"Zero" is a value. It is the unique, known quantity of zero, which is meaningful in arithmetic and other math.
"Null" is a non-value. It is a "placeholder" for a data value that is not known or not specified. It is only meaningful in this context; mathematical operations cannot be performed on null (the result of any such operation is undefined, and therefore also generally represented as null).
For example, as in the comments: "What is your yearly income?" is a question requiring a numeric answer. "0" is a perfectly valid answer for someone who does not work and has no investment income. If the user does not enter a value at all, they don't necessarily make no money; they just didn't want to tell your software how much (or little) they make. It's an unknown, not specified; therefore, to allow the software to continue, you specify the "null" placeholder for that data field within the software. That's technically valid from a data perspective; whether it's valid at the business level depends on whether an actual numeric value (even zero) is required in order to perform a mathematical operation (such as calculation of taxes, or comparison with thresholds determining benefits).
In computers, virtually any operation on a variable containing null will result either in null or in an error condition, because since one of the variable's values is not known, the result of the expression cannot be known. The equivalent of performing math on null would be if I asked you "What's five plus the number I'm thinking of right now?". It's impossible for you to give a definite answer because you don't know the number I'm thinking of. An operation on zero, except for dividing by it, is usually valid and will return another known, unique value.
Boss-speak is always tough...
Zero is a number so you can do things with it.
Null is a unicorn. It doesn't exist so you can't do anything at all with it.