NULL is nothing. It means theres nothing there. Often its just a place holder before something is there. Say u have a bunch of variables of animals. U might set them to NULL before u know what they are. Then u might check if they are NULL before u add an animal to them. Things are initialized as NULL. Answer from Draegan88 on reddit.com
W3Schools
w3schools.com › sql › sql_null_values.asp
SQL NULL Values - IS NULL and IS NOT NULL
ADD ADD CONSTRAINT ALL ALTER ALTER COLUMN ALTER TABLE ALTER VIEW AND ANY AS ASC BACKUP DATABASE BETWEEN CASE CHECK COLUMN CONSTRAINT CREATE CREATE DATABASE CREATE INDEX CREATE OR REPLACE VIEW CREATE TABLE CREATE PROCEDURE CREATE UNIQUE INDEX CREATE VIEW DATABASE DEFAULT DELETE DESC DISTINCT DROP DROP COLUMN DROP CONSTRAINT DROP DATABASE DROP DEFAULT DROP INDEX DROP TABLE DROP VIEW EXEC EXISTS FOREIGN KEY FROM FULL OUTER JOIN GROUP BY HAVING IN INDEX INNER JOIN INSERT INTO INSERT INTO SELECT IS NULL IS NOT NULL JOIN LEFT JOIN LIKE LIMIT NOT NOT NULL OR ORDER BY OUTER JOIN PRIMARY KEY PROCEDURE RIGHT JOIN ROWNUM SELECT SELECT DISTINCT SELECT INTO SELECT TOP SET TABLE TOP TRUNCATE TABLE UNION UNION ALL UNIQUE UPDATE VALUES VIEW WHERE MySQL Functions
Programmer's Wiki
code.fandom.com › wiki › Null
Null | Programmer's Wiki | Fandom
null (often NULL, or nil) is a constant used in many programming languages to indicate that the expected value is unknown. It is different from 0, the empty string, and false because these are known to be empty.
What is Null?
NULL is nothing. It means theres nothing there. Often its just a place holder before something is there. Say u have a bunch of variables of animals. U might set them to NULL before u know what they are. Then u might check if they are NULL before u add an animal to them. Things are initialized as NULL. More on reddit.com
60
34
July 5, 2024Need some knowledge on NULL and NOT NULL
a null is used for multiple purposes -- for example, not known, not applicable, etc. theoreticians take great joy in debating which uses are valid, and whether they can be substituted by some non-null placeholder suffice to say, a null is used when you don't know what value should go there if you don't want that situation to arise, just make the column NOT NULL and you'll never be able to not insert an actual value More on reddit.com
33
14
December 22, 2021language agnostic - What is the purpose of null? - Stack Overflow
Not having null would have been a TEN billion dollar mistake. Think about it: all pointers would have to be initialized to some 'valid' value, which when encountered would cause the program to happily keep on computing in the wrong context, leading to extremely hard-to-find bugs = worse than crash 2009-02-27T03:42:02.883Z+00:00 ... @Steven A. Lowe: That is ... More on stackoverflow.com
sql - NULL vs NOT NULL - Stack Overflow
In sql database column, empty fields will be set to NULL unless we specify it using NOT NULL. What are the advantages of using one instead of the other? Thanks! More on stackoverflow.com
02:07
SQL query to check IS Null and IS not Null data - YouTube
18:29
Constraints You Must Know: NOT NULL, DEFAULT, and CHECK Explained ...
06:54
SQL Tutorial #17 - SQL IS NULL and IS NOT NULL | SQL NULL Values ...
Null and Is Not Null
17:05
SQL NULL vs Empty String vs Blank Space (Visually Explained) | ...
53:00
SQL NULL Functions | COALESCE, ISNULL, NULLIF, IS (NOT) NULL | ...
Quora
quora.com › What-does-NULL-mean-in-programming-languages
What does NULL mean in programming languages? - Quora
Answer (1 of 6): null is the pointer or reference to address zero. Why would this be needed or used? Let’s say you are searching for a library book that you want to read. Unlike Amazon, your library doesn’t have every book. If you search for “Object Oriented Software Construction” by ...
Reddit
reddit.com › r/learnprogramming › what is null?
r/learnprogramming on Reddit: What is Null?
July 5, 2024 -
So I use C# and I often see many devs use null.
What and which kind of situation do you use this variable?
I am reading c# guide on programming book and I am on Clearing memory now and I haven't encountered null yet. Should I be worried?
Top answer 1 of 18
80
This was intended as a meme but is actually a good representation of what "Null" is. In C#, when you declare string s = "My shit"; it means that "s" is a reference to a memory location that holds the data "My shit". string s = null; means that the reference "s" exists but it's not pointing to any object, as in it holds nothing.
2 of 18
15
NULL is nothing. It means theres nothing there. Often its just a place holder before something is there. Say u have a bunch of variables of animals. U might set them to NULL before u know what they are. Then u might check if they are NULL before u add an animal to them. Things are initialized as NULL.
freeCodeCamp
freecodecamp.org › news › a-quick-and-thorough-guide-to-null-what-it-is-and-how-you-should-use-it-d170cea62840
A quick and thorough guide to ‘null’: what it is, and how you should use it
June 12, 2018 - As we can see, in case of a value type, the value itself is directly stored at the address A0A1 which is associated with variable name. There would be much more to say about reference versus value types, but this is out of the scope of this article. Please note also that some programming languages support only reference types, others support only value types, and some (e.g. C# and Java) support both of them. ... The concept of null exists only for reference types.
Zenva
gamedevacademy.org › home › software development › what is null in programming – complete guide
What Is Null In Programming - Complete Guide - GameDev Academy
November 21, 2023 - In programming, ‘null’ represents a null reference or a null pointer, which essentially means “no object” or “no value here”. It is a placeholder that signifies the absence of a value or a non-existent object.
Kotobas
kotobas.net › en › what-is-null
What is Null? - A Concise Explanation of Its Meaning and Concept - KOTOBAS
March 16, 2025 - In programming, it is used to denote that a variable or a pointer does not reference any valid data. Similar concepts are expressed by keywords such as Nil in Pascal, None in Python, and Nothing in VB.NET.
CodeItBro
codeitbro.com › home › glossaries › coding glossary › null
What is Null in Programming? Detailed Explaination
May 18, 2025 - This fundamentally differs from value types like integers or booleans, which cannot be null because they represent actual values rather than reference memory locations. The distinction between reference and value types is crucial for understanding ...
IBM
ibm.com › docs › en › informix-servers › 14.10.0
IS NULL and IS NOT NULL Conditions
Get assistance for the IBM products, services and software you own · Provides fixes and updates for your system's software, hardware, and operating system
Sololearn
sololearn.com › en › Discuss › 3240365 › what-is-the-difference-between-null-and-not-null
What is the difference between null and not null?
September 16, 2023 - sl_scroll_/de/Discuss/1859260/what-is-deffernce-between-software-engineering-and-computer-sciencePending · Maximum Storage Duration: SessionType: HTML Local Storage ... sl_scroll_/de/Discuss/1943908/essential-programming-languages-for-electrical-engineering-studentsPending · Maximum Storage Duration: SessionType: HTML Local Storage · sl_scroll_/de/Discuss/1953300/python-artificial-intelligence-Pending
Reddit
reddit.com › r/sql › need some knowledge on null and not null
r/SQL on Reddit: Need some knowledge on NULL and NOT NULL
December 22, 2021 -
-
Where and why exactly a null is used?
-
What is exactly null and not null? To my understanding Not null we use when its mandatory to insert some value in that field, also when we give check constraint so by default the column will be not null right?
-
By adding new column through alter method default values are null, so how would I be able to insert values in it and is it right to give not null constraint to that new column while adding through alter method, basically when null and when not null to be used?...
god this is so confusing please help me, ik im asking alot but im really confused
Top answer 1 of 5
8
a null is used for multiple purposes -- for example, not known, not applicable, etc. theoreticians take great joy in debating which uses are valid, and whether they can be substituted by some non-null placeholder suffice to say, a null is used when you don't know what value should go there if you don't want that situation to arise, just make the column NOT NULL and you'll never be able to not insert an actual value
2 of 5
3
Thoughts in this can vary but I'll give my input. NULL should be used where it is known that there can definitely be no value. If a person's record has an optional telephone number when signing up to a website, and they do not complete a number upon their submission, then a NULL is a valid value. However, if we are utilising something like "effective from" and "effective to" of a row of data, then effective to should never be NULL, we always determine that a row is either currently effective, or is historic and superceded. As a result, the "active" row should not hold a NULL in effective to, even though it is not known. It should be a future, default date, and the column should be set with a NOT NULL constraint.
Top answer 1 of 16
49
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 couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years. In recent years, a number of program analysers like PREfix and PREfast in Microsoft have been used to check references, and give warnings if there is a risk they may be non-null. More recent programming languages like Spec# have introduced declarations for non-null references. This is the solution, which I rejected in 1965.
2 of 16
32
null is a sentinel value that is not an integer, not a string, not a boolean - not anything really, except something to hold and be a "not there" value. Don't treat it as or expect it to be a 0, or an empty string or an empty list. Those are all valid values and can be geniunely valid values in many circumstances - the idea of a null instead means there is no value there.
Perhaps it's a little bit like a function throwing an exception instead of returning a value. Except instead of manufacturing and returning an ordinary value with a special meaning, it returns a special value that already has a special meaning. If a language expects you to work with null, then you can't really ignore it.
Top answer 1 of 5
12
If you need to represent unknown data in a column, you make it nullable. If you will always have data in the column, it's better to make it not nullable, as
- Dealing with nulls can be annoying and counterintuitive
- It saves a bit of space
- On some database systems, null values are not indexed.
2 of 5
3
When a field is set to NOT NULL, it cannot be empty. Which means you have to specify a value for that field when inserting a record.
Medium
medium.com › @shlomohassid › null-how-do-you-define-nothing-and-why-would-you-07683bdbe63a
NULL: How Do You Define Nothing? And Why Would You? | by Momi | Medium
May 31, 2025 - No true NULL at hardware level: As mentioned, hardware doesn’t have a dedicated notion of a null pointer. The CPU simply sees the address 0x0 like any other number. What makes 0 special is how software (and the operating system) treats it. In most operating systems, address 0 resides in a protected region of memory. The OS deliberately does not map any valid memory to address 0 (or often, to the entire first page of memory). This means if a program tries to read or write memory at address 0, the CPU will raise a fault (because the memory management unit says “no valid memory here”) and the program will crash.
DevX
devx.com › home › null
Null - DevX
January 17, 2024 - The technology term “null” is important because it represents the concept of an empty or non-existent value in various programming languages and field of technology. In programming languages such as JavaScript, C, and Java, a null value can be assigned to variables to indicate that they do not have a valid object reference or lack any value or data.
Sololearn
sololearn.com › en › discuss › 1326682 › what-is-the-difference-between-null-and-not-null
What is the difference between null and not null | Sololearn: Learn to code for FREE!
June 5, 2018 - And Not Null means you can't leave the value of that field empty. E. g when you fill a form online, there is an asterisk(*) shown near Name field, password, etc., so that field is not null, those values are important and should be filled.
W3Schools
w3schools.com › sql › sql_notnull.asp
SQL NOT NULL Constraint
ADD ADD CONSTRAINT ALL ALTER ALTER COLUMN ALTER TABLE ALTER VIEW AND ANY AS ASC BACKUP DATABASE BETWEEN CASE CHECK COLUMN CONSTRAINT CREATE CREATE DATABASE CREATE INDEX CREATE OR REPLACE VIEW CREATE TABLE CREATE PROCEDURE CREATE UNIQUE INDEX CREATE VIEW DATABASE DEFAULT DELETE DESC DISTINCT DROP DROP COLUMN DROP CONSTRAINT DROP DATABASE DROP DEFAULT DROP INDEX DROP TABLE DROP VIEW EXEC EXISTS FOREIGN KEY FROM FULL OUTER JOIN GROUP BY HAVING IN INDEX INNER JOIN INSERT INTO INSERT INTO SELECT IS NULL IS NOT NULL JOIN LEFT JOIN LIKE LIMIT NOT NOT NULL OR ORDER BY OUTER JOIN PRIMARY KEY PROCEDURE RIGHT JOIN ROWNUM SELECT SELECT DISTINCT SELECT INTO SELECT TOP SET TABLE TOP TRUNCATE TABLE UNION UNION ALL UNIQUE UPDATE VALUES VIEW WHERE MySQL Functions
Medium
medium.com › @sumeet2703 › understanding-the-difference-between-zero-and-null-in-programming-db60b4e12934
Understanding the Difference Between Zero and Null in Programming | by Sumeet K | Medium
September 4, 2024 - It is not a number, nor is it a default value—it signifies that a variable has not been assigned any value at all. Different programming languages handle null (or its equivalents) in various ways, but the concept remains consistent:
Reddit
reddit.com › r/csharp › !=null , is not null
r/csharp on Reddit: !=null , is not null
November 25, 2024 -
What's the difference and why works one be used in preference over the other , and when would you not use one of them?
Top answer 1 of 5
211
!= invokes the operator, which might do anything. Is not null always compares against null.
2 of 5
53
!= can be overridden. is (not) can not be overridden. So if you do (myClass != null) it can be true even if myClass is null because the != operator could be overridden. That can't happen with (myClass is not null) because it can not be overridden.
TechCareer
techcareer.net › en › dictionary › null
What is Null? What does it do?
Null shows that an object or reference does not contain any data or does not point to an object. For instance, in languages like Java and C#, null is used to indicate that an object reference does not point to a valid object.