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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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  • c# - What does null! statement mean? - Stack Overflow
    It can be used on a type to control Nullability, it is then called the "Null Forgiving Operator" Basically, null! applies the ! operator to the value null This overrides the nullability of the value null to non-nullable, telling the compiler that null is a "non-null" type
  • Why does NULL = NULL evaluate to false in SQL server
    The expression "NULL = NULL" evaluates to NULL, but is actually invalid in SQL; yet ORDER BY treats NULLs as equal (whatever they precede or follow "regular" values is left to DBMS vendor)
  • 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
  • javascript - Why is null an object and whats the difference between . . .
    In order to be able to query this difference, JavaScript has null and undefined: While null is - just like in other languages an object, undefined cannot be an object because there is no instance (even not a null instance) available
  • What is the purpose of null? - Stack Overflow
    Null: The Billion Dollar Mistake Tony Hoare: I call it my billion-dollar mistake It was the invention of the null reference in 1965 At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W) My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler But I
  • What is null in Java? - Stack Overflow
    What is null? Is null an instance of anything? What set does null belong to? How is it represented in the memory?
  • 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
  • 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)
  • sql - Not equal lt; gt; != operator on NULL - Stack Overflow
    135 NULL has no value, and so cannot be compared using the scalar value operators In other words, no value can ever be equal to (or not equal to) NULL because NULL has no value Hence, SQL has special IS NULL and IS NOT NULL predicates for dealing with NULL
  • 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





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