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NULL    音标拼音: [n'ʌl]
n. 空,零迅号,零
a. 无效力的,无效的,无价值的

空,零迅号,零无效力的,无效的,无价值的

null
空的; 空; 无; 零; 空白; 虚字; 空( 字元 ) NUL

null
空

null
adj 1: lacking any legal or binding force; "null and void" [synonym:
{null}, {void}]
n 1: a quantity of no importance; "it looked like nothing I had
ever seen before"; "reduced to nil all the work we had
done"; "we racked up a pathetic goose egg"; "it was all for
naught"; "I didn't hear zilch about it" [synonym: {nothing},
{nil}, {nix}, {nada}, {null}, {aught}, {cipher}, {cypher},
{goose egg}, {naught}, {zero}, {zilch}, {zip}, {zippo}]

Null \Null\, v. t. [From null, a., or perh. abbrev. from annul.]
To annul. [Obs.] --Milton.
[1913 Webster]


Null \Null\, n. [Etymol. uncertain.]
One of the beads in {nulled work}.
[1913 Webster]


Null \Null\, a. [L. nullus not any, none; ne not ullus any, a
dim. of unus one; cf. F. nul. See {No}, and {One}, and cf.
{None}.]
1. Of no legal or binding force or validity; of no efficacy;
invalid; void; nugatory; useless.
[1913 Webster]

Faultily faultless, icily regular, splendidly null,
Dead perfection; no more. --Tennyson.
[1913 Webster]

2. Having a value of zero; as, of null utility.
[PJC]

3. (Math.) Empty; having no members; as, the null set.
[PJC]

4. (Computers) Unassigned or meaningless; -- a special value
given to variables, especially pointers or logical
variables, indicating that it is meaningless and cannot be
used in computation; as, an uninitialized pointer in "C"
is given a null value. The actual value that is stored in
memory to indicate the null condition may vary with the
computer language used.
[PJC]


Null \Null\, n.
1. Something that has no force or meaning.
[1913 Webster]

2. That which has no value; a cipher; zero. --Bacon.
[1913 Webster]

{Null method} (Physics.), a zero method. See under {Zero}.
[1913 Webster]

51 Moby Thesaurus words for "null":
aimless, bad, bare, barren, bland, blank, bleached, characterless,
clear, designless, devoid, empty, existless, featureless, garbled,
hollow, importless, inane, ineffective, ineffectual, inefficacious,
insignificant, insipid, invalid, lacking, meaningless, minus,
missing, negative, nonconnotative, nondenotative, nonexistent,
null and void, phatic, purportless, purposeless, scrambled,
senseless, unexisting, unmeaning, unrelieved, unsignificant,
useless, vacant, vacuous, void, white, with nothing inside,
without being, without content, worthless

A special value used in several languages to
represent the thing referred to by an uninitialised pointer.

A special value that may be stored in some database
columns to represent an unknown, missing, not applicable, or
undefined value. Nulls are treated completely differently
from ordinary values when evaluating SQL expressions and there
are several SQL constructs for dealing with nulls.

(2003-06-17)


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  • SQL is null and = null - Stack Overflow
    The reasoning is that a null means "unknown", so the result of any comparison to a null is also "unknown" So you'll get no hit on rows by coding where my_column = null SQL provides the special syntax for testing if a column is null, via is null and is not null, which is a special condition to test for a null (or not a null)
  • What is the difference between is not null and != null?
    The main difference between e != null and e is not null is the way the the compiler executes the comparison Microsoft: "The compiler guarantees that no user-overloaded equality operator == is invoked when expression x is null is evaluated " Bottom Line: If you are writing code that you don't want to depend on someone's implementation of the != and == operators, use is null and is not null
  • Whats the difference between = null and IS NULL?
    Understanding the difference between “IS NULL” and “= NULL” When a variable is created in SQL with the declare statement it is created with no data and stored in the variable table (vtable) inside SQLs memory space The vtable contains the name and memory address of the variable
  • How do I check for null values in JavaScript? - Stack Overflow
    How can I check for null values in JavaScript? I wrote the code below but it didn't work
  • Null object in Python - Stack Overflow
    How do I refer to the null object in Python?
  • How to send NULL in HTTP query string? - Stack Overflow
    So if you don't need to support the difference between empty and null absent string you may also consider the empty parameter as null If instead you want to recreate point 4 of JSON {"param":null} with request parameters you must use a convention, like passing %00 as suggested in the answers or using the null marker parameter I propose later
  • javascript - Why is null an object and whats the difference between . . .
    The surprise expressed by JavaScript developers at typeof null === "object" is the result of an impedance mismatch (or abstraction leak) between a weakly-typed language (JavaScript) that has both null and undefined, and another, strongly-typed language (Java) that only has null, and in which null is strictly defined to refer to a reference type
  • What exactly is meant by dereferencing a NULL pointer?
    In other words, a null pointer is a pointer of any type pointing at a well-defined "nowhere" Any pointer can turn into a null pointer when it is assigned a null pointer constant The standard mentions 0 and (void*)0 as two valid null pointer constants, but note that it says "an integer constant expression with the value 0 "
  • How do I create a unique constraint that also allows nulls?
    I want to have a unique constraint on a column which I am going to populate with GUIDs However, my data contains null values for this columns How do I create the constraint that allows multiple n
  • How can I check for an undefined or null variable in JavaScript?
    96 Checking null with normal equality will also return true for undefined if (window variable == null) alert('variable is null or undefined');





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