W3Schools
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SQL NULL Values - IS NULL and IS NOT NULL
It is not possible to test for NULL values with comparison operators, such as =, <, or <>. We will have to use the IS NULL and IS NOT NULL operators instead. SELECT column_names FROM table_name WHERE column_name IS NULL; SELECT column_names FROM table_name WHERE column_name IS NOT NULL; Below is a selection from the Customers table used in the examples:
MDN Web Docs
developer.mozilla.org โบ en-US โบ docs โบ Web โบ JavaScript โบ Reference โบ Operators โบ null
null - JavaScript | MDN
typeof null; // "object" (not "null" for legacy reasons) typeof undefined; // "undefined" null === undefined; // false null == undefined; // true null === null; // true null == null; // true !null; // true Number.isNaN(1 + null); // false Number.isNaN(1 + undefined); // true
Videos
01:03:16
How to handle NULL in SQL - YouTube
02:48
Database Systems - NULL Values - YouTube
03:19
Null Values - YouTube
03:28
Definition: What is a Null Value? - YouTube
04:46
Understanding NULL Values in SQL | What NULL Means and How to Use ...
01:00
What are NULL values? - YouTube
special marker and keyword in SQL indicating that something has no value
Factsheet
Null (SQL)
Notation ฯ
Null (SQL)
Notation ฯ
Wikipedia
en.wikipedia.org โบ wiki โบ Null_(SQL)
Null (SQL) - Wikipedia
January 7, 2026 - In an Oracle RDBMS, for example, NULL and the empty string are considered the same thing and therefore 'Fish ' || NULL || 'Chips' results in 'Fish Chips'. Since Null is not a member of any data domain, it is not considered a "value", but rather a marker (or placeholder) indicating the undefined ...
HistoryNull propagationComparisons with NULL and the three-valued logic (3VL)Analysis of SQL Null missing-value semanticsCheck constraints and foreign keysOuter joinsAggregate functionsWhen two nulls are equal: grouping, sorting, and some set operationsEffect on index operationNull-handling functionsData typing of Null and UnknownBOOLEAN data typeControversyFurther reading
Microsoft Learn
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Handling Null Values - ADO.NET | Microsoft Learn
Use the IS NULL or IS NOT NULL predicate to test for a null value. This can add complexity to the WHERE clause. For example, the TerritoryID column in the AdventureWorks Customer table allows null values.
Reddit
reddit.com โบ r/learnprogramming โบ 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?
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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.
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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.
GeeksforGeeks
geeksforgeeks.org โบ sql โบ sql-null-values
NULL values in SQL - GeeksforGeeks
May 2, 2017 - Attribute Not Applicable: The value is undefined for a specific record. Setting a NULL value is appropriate when the actual value is unknown, or when a value is not meaningful.
Tutorialspoint
tutorialspoint.com โบ home โบ sql โบ sql null values
Understanding SQL NULL Values
November 29, 2009 - The value is not yet known. Since the NULL values are basically non-existent, you cannot use comparison operators such as = , <, or > with them.
DbSchema
dbschema.com โบ blog โบ tutorials โบ sql-null-values
SQL NULL Values Explained with Examples
Using = NULL instead of IS NULL: As mentioned earlier, = NULL does not work as expected. Always use IS NULL to check for NULL values. Treating NULL as an empty string or zero: NULL is a special marker and should not be confused with an empty string or zero.
Biztory
biztory.com โบ blog โบ 7-things-you-should-know-about-null-values
7 Things to know about NULL values - Biztory | Biztory
October 25, 2025 - If a value appears suspiciously often or seems impossible; it might be an attempt to input NULL values. ... Just to name a couple of examples: I once saw a database where all of the customers who made a purchase before 2005 had an age of 27.
freeCodeCamp
freecodecamp.org โบ news โบ a-quick-and-thorough-guide-to-null-what-it-is-and-how-you-should-use-it-d170cea62840
A quick and thorough guide to โnullโ: what it is, and how you should use it
June 12, 2018 - The basic rule is simple: null should only be allowed when it makes sense for an object reference to have 'no value associated with it'. (Note: an object reference can be a variable, constant, property (class field), input/output argument, and so on.) For example, suppose type person with fields name and dateOfFirstMarriage:
Navicat
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The NULL Value and its Purpose in Relational Database Systems
When writing queries, there are times that you'll want to filter out rows with NULL values. Other times, you'll specifically want to retrieve rows that contain NULLs. Here's how to do both: Queries can filter out nulls using the IS NOT NULL clause. Here's an example that excludes films from the Sakila database that contain a NULL original_language_id:
MariaDB
mariadb.com โบ docs โบ server โบ reference โบ data-types โบ null-values
NULL Values | Server | MariaDB Documentation
When a table is created or the format altered, columns can be specified as accepting NULL values, or not accepting them, with the NULL and NOT NULL clauses respectively. For example, a customer table could contain dates of birth.
DataLemur
datalemur.com โบ sql-tutorial โบ sql-null
Handling NULL Values | DataLemur
In the realm of databases, values ... Employee Records: In a human resources database, some employees might not have entered their emergency contact information yet, resulting in NULL values in that column....
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In simple worlds you can say that Null is not a data value, but a marker for an unknown value.
So any mathematical operations performed on NULL will result in NULL. For example,
10 + NULL = NULL
Similarly if you do string concatenation with string you get:-
'String ' || NULL || 'Concatenation' -- Result is NULL
So you can say that Null means either "not applicable" or "don't know": it is not the same as zero (0) or any other default value, but more importantly, null is treated quite differently from other values in SQL, because it literally has no value.
An example to explain what it means when we say that NULL means UNKNOWN VALUE:
StudentName TestResult
X 78
A 89
B 67
C NULL
So you can see that the student C got NULL marks in the test. So what does that mean?
Now one can say that the student does not sit in the test or it may be that the student's data is not avaialable. But it definitely does not mean that the student got 0(as if you assign 0 to the student then it would mean that the student appeared in the test and got zero) marks in the test. All we can say that the data for the student is
UNKNOWN or NULL
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A field with a NULL value is a field with no value. It is very important to understand that a NULL value is different than a zero value or a field that contains spaces.
If a column in a table is optional, we can insert a new record or update an existing record without adding a value to this column. This means that the field will be saved with a NULL value.
NULL values are treated differently from other values.
NULL is used as a placeholder for unknown or inapplicable values. Read more about this here.
Khoury College of Computer Sciences
khoury.northeastern.edu โบ home โบ kenb โบ MeaningOfNull.html
The Meaning of Null in Databases and Programming Languages
There are a number of variations on this. Here are a few of them: The value does exist somewhere, but the database does not have it. The value has not yet been determined, but it presumably will be determined at some point. For example, a customer has yet to make a decision about a feature.
Modern SQL
modern-sql.com โบ concept โบ null
Modern SQL: NULL โ purpose, comparisons, NULL in expressions, mapping to/from NULL
For example, the SQL language itself uses the null value for the absent values resulting from an outer join.2 Although exceptions exist,3 it is not generally possible to tell why ...
DB Vis
dbvis.com โบ thetable โบ the-definitive-guide-to-the-null-sql-server-value
The Definitive Guide to the NULL SQL Server Value
September 12, 2024 - For example, assume a column for a middle name is nullable. In this case, NULL values indicate that the person either does not have a middle name or this information has not been provided yet.
Microsoft Learn
learn.microsoft.com โบ en-us โบ dotnet โบ csharp โบ language-reference โบ keywords โบ null
null keyword - C# reference | Microsoft Learn
Console.WriteLine($"t.Equals(s) is {t.Equals(s)}"); // Equality operator also returns false when one // operand is null. Console.WriteLine($"Empty string {(s == t ? "equals" : "does not equal")} null string"); // Returns true. Console.WriteLine($"null == null is {null == null}"); // A value type cannot be null // int i = null; // Compiler error!
MySQL
dev.mysql.com โบ doc โบ refman โบ 8.4 โบ en โบ null-values.html
MySQL :: MySQL 8.4 Reference Manual :: 11.1.7 NULL Values
For sorting with ORDER BY, NULL values sort before other values for ascending sorts, after other values for descending sorts.