W3Schools
w3schools.com › sql › sql_null_values.asp
SQL NULL Values - IS NULL and IS NOT NULL
It is not a value itself, but a placeholder to indicate the absence of data. Note: A NULL value is different from zero (0) or an empty string ('').
special marker and keyword in SQL indicating that something has no value
Factsheet
Null (SQL)
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Null (SQL)
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Wikipedia
en.wikipedia.org › wiki › Null_(SQL)
Null (SQL) - Wikipedia
20 hours ago - This means that a check constraint will succeed if the result of the check is either True or Unknown. The following example table with a check constraint will prohibit any integer values from being inserted into column i, but will allow Null to be inserted since the result of the check will always evaluate to Unknown for Nulls.
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
Where do NULL values come from in datasets and how to handle them?
It is fine to have null values in data sets. If something can be NULL you are saying, it’s okay to not have it. You just need to make sure that when operating on something that could be null you are checking before operating on it. If(possiblyNullValue) {console.log(“it’s not null”)} More on reddit.com
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June 8, 2024What is Null?
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. More on reddit.com
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July 5, 2024Videos
02:48
Database Systems - NULL Values - YouTube
01:00
What are NULL values? - YouTube
03:28
Definition: What is a Null Value? - YouTube
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Understanding NULL Values in SQL | What NULL Means and How to Use ...
01:03:16
How to handle NULL in SQL - YouTube
06:54
SQL Tutorial #17 - SQL IS NULL and IS NOT NULL | SQL NULL Values ...
Navicat
navicat.com › en › company › aboutus › blog › 1312-the-null-value-and-its-purpose-in-relational-database-systems
The NULL Value and its Purpose in Relational Database Systems
March 3, 2020 - This is what is commonly referred to as a "null pointer". In a database, zero is a value which has meaning, so the value NULL became is a special marker to mean that no value exists.
Biztory
biztory.com › home › blog › 7 things you should know about null values
7 Things to know about NULL values - Biztory | Biztory
October 25, 2025 - Unfortunately, it is very common ... NULL values and other special markers (e.g. NaN, NA, Inf) might be cast into strings and treated like any other text field. This is particularly problematic because certain commands like IS NULL or LEN(0) won't work anymore, meaning you should ...
Reddit
reddit.com › r/learnprogramming › where do null values come from in datasets and how to handle them?
r/learnprogramming on Reddit: Where do NULL values come from in datasets and how to handle them?
June 8, 2024 -
My understanding is that NULL represents true absence of value or a total unknown value. This is not the same as empty which is a known value, or a string of zero length. I've worked with banking data and often see lots of NULL values in various fields but if NULL represents UNKNOWN does that mean something simply went wrong/error in the system or is it a legitimate value? Because otherwise I'd think putting empty there makes more sense.
Not really sure how to treat NULL values in these datasets, should I simply ignore them? What if I'm trying to transform the data (or preform joins) on these rows wouldn't NULL values throw all the calculations off?
How should I think about and handle NULL values as they come into my codebase?
Thanks
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It is fine to have null values in data sets. If something can be NULL you are saying, it’s okay to not have it. You just need to make sure that when operating on something that could be null you are checking before operating on it. If(possiblyNullValue) {console.log(“it’s not null”)}
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NULL values can mean whatever you want them to mean, and different people have different opinions on how they should be used. Generally, the only way they will enter your database is because you insert them -- either explicitly by using NULL as a value in an INSERT statement, or implicitly, by not specifying a value for a column whose default is NULL. Probably the most common reason to use NULL is to represent an "optional" value. For instance, maybe in a banking application, you have a user table with a "social security number" field. Some of your users might be US residents who have an SSN, and others might be foreigners who don't. This could be considered a "true absence of value" because it's not the case that the person has an SSN which is "empty", they simply don't have one. It doesn't necessarily make sense to allow a "missing" or NULL value for every field, which is why databases allow you to easily declare which fields are nullable or non-nullable in your schema. Can you explain why you think using NULL would "throw all the calculations off"? It's true that NULL has different behavior than an empty string, but that might be exactly what you want. For instance, if you perform a join on the SSN field, you probably wouldn't want every possible pair of users with a missing SSN to be joined with each other. Two empty strings are considered "equal", but two NULL values are not.
GeeksforGeeks
geeksforgeeks.org › sql › sql-null-values
NULL values in SQL - GeeksforGeeks
January 5, 2026 - Some records in an SQL table may not have values for every field, and such fields are termed NULL values. These occur when data is unavailable during entry or when an attribute does not apply to a specific record.
Khoury College of Computer Sciences
khoury.northeastern.edu › home › kenb › MeaningOfNull.html
The Meaning of Null in Databases and Programming Languages
For the rest of this article, I will use the convention that "NULL" (all uppercase letters) means "database null" and "null" (all lowercase letters) means "programming language null". One consequence of defining NULL differently from null is that one cannot use ordinary Boolean logic. The result of a logical expression now has three possible values rather than just two.
IBM
ibm.com › docs › en › rbd › 9.6.0
Null values and the nullable type - IBM Documentation
February 10, 2022 - Technically a null value is a reference (called a pointer in some languages) to an empty area of memory. Reference variables (variables that contain an address for data rather than the data itself) are always nullable, which means they are automatically capable of having a null value.
TheFreeDictionary.com
thefreedictionary.com › Null+value
Null value - definition of Null value by The Free Dictionary
Null value synonyms, Null value pronunciation, Null value translation, English dictionary definition of Null value. adj. 1. Having no legal force; invalid: render a contract null and void. 2. Of no consequence, effect, or value; insignificant.
Essential SQL
essentialsql.com › home › what is a database null value?
What is a Database NULL Value? - Essential SQL
March 4, 2023 - When it isn’t possible to specially code your data using “N/A” you can use the special keyword NULL to denote a missing value. NULL is tricky. NULL isn’t a value in the normal sense. For instance no two NULL are equal to each other.
Esri Support
support.esri.com › en-us › gis-dictionary › null-value
Null Value Definition | GIS Dictionary
The absence of a recorded value for a field. A null value differs from a value of zero in that zero may represent the measure of an attribute, while a null value indicates that no measurement has been
MSSQLTips
mssqltips.com › home › sql null meaning and how to handle null values
SQL NULL Meaning and How to Handle NULL Values
June 20, 2024 - It is important to understand that NULL is not the same as 0 for numbers or an empty string for character-based data types. It is also not the word “NULL.” NULL is completely separate and follows different rules than non-null values.
DB Vis
dbvis.com › thetable › the-definitive-guide-to-the-null-sql-server-value
The Definitive Guide to the NULL SQL Server Value
September 12, 2024 - For this reason, SQL Server allows columns to be defined as nullable. The NULL SQL Server value acts as a special placeholder to represent the absence of data in a structured and meaningful way.
MDN Web Docs
developer.mozilla.org › en-US › docs › Glossary › Null
Null - Glossary - MDN Web Docs
In computer science, a null value represents a reference that points, generally intentionally, to a nonexistent or invalid object or address. The meaning of a null reference varies among language implementations.
Microsoft Learn
learn.microsoft.com › en-us › dotnet › framework › data › adonet › sql › handling-null-values
Handling Null Values - ADO.NET | Microsoft Learn
September 15, 2021 - A null value in a relational database is used when the value in a column is unknown or missing. A null is neither an empty string (for character or datetime data types) nor a zero value (for numeric data types).
Tutorialspoint
tutorialspoint.com › sql › sql-null-values.htm
SQL - NULL Values
SQL uses the term NULL to represent a non-existent data value in the database. These values are not the same as an empty string or a zero. They don't hold any space in the database and are used to signify the absence of a value or the unknown value
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 - Instead, they use the Maybe/Optional ... cannot occur. ... If a reference points to null, it always means that there is no value associated with it....
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?
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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.
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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.