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
July 24, 2026 - In the SQL database query language, null or 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 ...
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
W3Schools
w3schools.com › sql › sql_null_values.asp
SQL NULL Values - IS NULL and IS NOT NULL
If a field in a table is optional, ... field will be saved with a NULL value. A NULL value represents an unknown, missing, or inapplicable data in a database field....
What is NULL in SQL? - Stack Overflow
NULL is a value used to indicate that there is no domain specific value in the field. But I would still say that NULL itself is a value. Just try to ask a database admin what the default value is of a field, if no value is provided. More on stackoverflow.com
What 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, 2022Need 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
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December 22, 2021What type of integrity constraint is NOT NULL?
Data types are not considered a constraint in SQL. NOT NULL is just part of the datatype. More on reddit.com
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June 29, 202404:27
Tutorial#27 How NULL value treated in Oracle SQL Database|IS NULL ...
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DBMS - Null Values in SQL - YouTube
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Null Values - YouTube
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How to Handle NULL Values in SQL Queries | Datamites - YouTube
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Understanding NULL Values in SQL | What NULL Means and How to Use ...
Khoury College of Computer Sciences
khoury.northeastern.edu › home › kenb › MeaningOfNull.html
The Meaning of Null in Databases and Programming Languages
The main distinction between the relational null and the programming language null is the following: The relational null represents the absence of a value in a field of a record; whereas the programming language null represents one of the possible values of a variable. Succinctly, Consequently, the phrase "null value" is an oxymoron for databases.
GeeksforGeeks
geeksforgeeks.org › sql › sql-null-values
NULL values in SQL - GeeksforGeeks
January 5, 2026 - To handle such scenarios, SQL provides ... a NULL value differs from a zero or an empty string. A NULL value represents missing or undefined data....
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!
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).
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.
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 ...
LearnSQL.com
learnsql.com › blog › what-is-null-in-sql
What Is a NULL in SQL? | LearnSQL.com
March 17, 2021 - NULL is used for fields with unknown or inapplicable values. It's different from an empty or zero value. No two NULL values are equal. Any field in a table can be defined to allow (or not allow) NULL values, regardless of the data type.
Enki
enki.com › post › understanding-null-values-in-sql
Enki | Blog - Understanding NULL Values in SQL
NULL in SQL is a special marker used to indicate that a data value does not exist in the database.
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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.
Oracle
docs.oracle.com › en › database › oracle › oracle-database › 26 › sqlrf › Nulls.html
Nulls
1 week ago - Nulls can appear in columns of any data type that are not restricted by NOT NULL or PRIMARY KEY integrity constraints. Use a null when the actual value is not known or when a value would not be meaningful. The database treats a character value with a length of zero as null.
Tencent Cloud
tencentcloud.com › techpedia › 133696
What does null value mean in a database? - Tencent Cloud
December 31, 2025 - Instead, it indicates that the data is missing, not applicable, or simply not provided for a particular record. For example, consider a database table named Employees with the following columns: EmployeeID, Name, Department, and Salary. If an employee has not yet been assigned to a department, the Department field for that employee might be set to null, meaning the department information is currently unavailable or not applicable.
Reddit
reddit.com › r/learnsql › what is a null in sql? is it the same as a empty cell?
r/learnSQL on Reddit: What is a null in sql? is it the same as a empty cell?
October 5, 2022 -
Lets say i have a Excel sheet , col : name and ID . some rows cells in "name" are empty in datasheet.
now sql pulls this data, will the empty cells be filled with a null value by default?
or is null a unique type of character that is only used to overwrite existing values , so when system reads it it thinks its empty?
Top answer 1 of 5
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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.
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NULL Is not equal to empty cell. Empty cells can sometimes contain space in the cell and you'll not be able to filter these out with NULL For Empty cells you could use LEN() in Excel.
Wordpress
datatechnologytoday.wordpress.com › 2017 › 07 › 18 › what-the-null-handling-missing-information-in-database-systems
What the Null? Handling Missing Information in Database Systems | Data and Technology Today
July 18, 2017 - In relational database systems, a null represents missing or unknown information at the column level. A null is not the same as 0 (zero) or blank. Null means no entry has been made for the column and it implies that the value is either unknown ...
DB Vis
dbvis.com › thetable › working-with-null-in-databases-turn-your-frustration-into-delight
Working with NULL in Databases: Turn Frustration Into Delight
July 5, 2024 - Many database administrators set NULL as the default value of their columns when creating a table by running a query like so: Assigning the default value of columns in DbVisualizer · Now when any data is inserted into the column named column_1, the default – “pre-built” if you will – value will be NULL.
Medium
medium.com › the-table-sql-and-devtalk › demystifying-null-values-in-databases-3bf63967fc30
Understand and Manage NULL in Databases | The Table — Databases and SQL
January 16, 2025 - Partitioning data can be tricky when NULL is involved. MySQL treats NULL as a "smallest value" and has specific rules for where NULL values are stored. Many mistake NULL for an empty string, but they’re not the same. An empty string is a value, while NULL represents "no value." NULLs use minimal storage but may occupy extra space depending on the database engine.
DbSchema
dbschema.com › blog › tutorials › sql null values: is null, coalesce, nullif, and common pitfalls | dbschema
SQL NULL Values: IS NULL, COALESCE, NULLIF, and Common Pitfalls | DbSchema
August 22, 2023 - In MySQL, PostgreSQL, and SQL Server an empty string is a value that happens to have no characters, so it can be compared and two empty strings are equal. NULL is the absence of a value, so a comparison with it is UNKNOWN instead.