special marker and keyword in SQL indicating that something has no value
Factsheet
Null (SQL)
Notation ω
Null (SQL)
Notation ω
Wikipedia
en.wikipedia.org › wiki › Null_(SQL)
Null (SQL) - Wikipedia
1 week ago - NULL is a special marker used to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL null serves to fulfill the requirement that all true relational database management systems (RDBMS) support a representation ...
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
GeeksforGeeks
geeksforgeeks.org › sql › sql-null-values
NULL values in SQL - GeeksforGeeks
January 5, 2026 - A NULL value represents missing or undefined data. Since it is often not possible to determine which interpretation applies, SQL treats all NULL values as distinct and does not distinguish between them.
What is NULL in SQL? - Stack Overflow
Just try to ask a database admin what the default value is of a field, if no value is provided. And he will most likely answer null. ... 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, ... So you can say that Null means ... More on stackoverflow.com
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, 2024Why in firebase rules exists() function gives me a null value error? any help is greatly appreciated.
If no user is signed in, request.auth is null. I think adding request.auth != null && in front of the exist should prevent that issue. Rules applied to a document are not inherited by their child documents. Therefor the check within hostels is not enough (afaik). More on reddit.com
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June 8, 2022What is a null in sql? is it the same as a empty cell?
NULL, in simplest terms, is the absence of data. Not to be confused with '', an empty string. If you are familiar with other languages, you could think of it as similar to undefined, in that the column has a type defined, but the specific cell has no data, and is more of a place holder for future data. When filtering for NULL, you will need to do things like table.col is null or table.col is not null In your Excel example, it depends on how you import the data, and what the definition of the target table is. The target table may have rules built into it to default the data for certain columns, or reject NULL values from other columns. You could have Null, an empty string, zero, weird dates.. etc. More on reddit.com
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October 5, 2022Videos
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. In addition to TRUE and FALSE, one must now admit the possibility of NULL.
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 - A NULL value is a special marker used in SQL to indicate that a data value does not exist in the database. In other words, it is just a placeholder to denote values that are missing or that we do not know.
W3Schools
w3schools.com › sql › sql_null_values.asp
SQL NULL Values - IS NULL and IS NOT NULL
A NULL value represents an unknown, missing, or inapplicable data in a database field.
Essential SQL
essentialsql.com › home › what is a database null value?
What is a Database NULL Value? - Essential SQL
March 4, 2023 - A null value is used in databases to signify a missing or unknown value. A NULL can be tricky. NULL = NULL is false!
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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.
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).
LearnSQL.com
learnsql.com › blog › what-is-null-in-sql
What Is a NULL in SQL? | LearnSQL.com
March 17, 2021 - An SQL NULL value is a flag that signals the lack of a value for a data field. Learn how to work with it in SQL queries.
Microsoft Learn
learn.microsoft.com › en-us › sql › t-sql › language-elements › null-and-unknown-transact-sql
NULL and UNKNOWN (Transact-SQL) - SQL Server | Microsoft Learn
Null values generally indicate data that is unknown, not applicable, or to be added later. For example, a customer's middle initial might not be known at the time the customer places an order.
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
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.
Enki
enki.com › post › understanding-null-values-in-sql
Enki | Blog - Understanding NULL Values in SQL
This distinction is important for understanding the integrity and behavior of database queries. Unlike a zero value, which indicates a known absence, or an empty string, which represents a present but empty value, NULL signifies the absence of any data value.
Quora
quora.com › What-is-the-definition-of-a-NULL-value-in-a-database-table-Is-it-normal-to-have-a-column-with-a-NULL-value
What is the definition of a NULL value in a database table? Is it normal to have a column with a NULL value? - Quora
Answer (1 of 2): A NULL value in relational database terms represents a value which is not known. It is not zero or space (blank) which are values, simply that the value is unknown.
DB Vis
dbvis.com › thetable › dealing-with-null-in-sql-complete-guide
Dealing With NULL in SQL: Complete Guide
April 9, 2025 - Handling NULL in SQL is a fundamental skill for anyone working with databases. NULL represents missing or unknown data, and it behaves differently from other values in SQL.
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.
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 - NULL isn’t a value but rather the absence of a value. That doesn’t always make sense to a newcomer. Let’s use an example to explain. I asked four people how much money they had in their wallets.
Oracle
docs.oracle.com › en › database › other-databases › timesten › 22.1 › sql-reference › null-values.html
Null Values
July 25, 2025 - The value NULL indicates the absence of a value. It is a placeholder for a value that is missing. Use a NULL when the actual value is not known or when a value would not be meaningful. Do not use NULL to represent a numeric value of zero, because they are not equivalent.