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.
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
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
rdbms - Null value in Database - Stack Overflow
Null value means No value Inapplicable,unassigned, unknown, or unavailable Which is true? More on stackoverflow.com
oop - Are nulls in a relational database okay? - Stack Overflow
There's a school of thought that null values should not be allowed in a relational database. That is, a table's attribute (column) should not allow null values. Coming from a software development More on stackoverflow.com
What are pros and cons of using NULLS vs NOTNULLs in database?
Pros of using NULL: When your column can be NULL, NULL is a perfect fit. Pros of using NOTNULL: When your column cannot be NULL, NOTNULL is a perfect fit. Cons of using NULL: When your column cannot be NULL, NOTNULL would be a better fit. Cons of using NOTNULL: When your column can be NULL, NULL would be a better fit. More on reddit.com
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March 15, 2022Is using `blank=True, null=True` a lot considered to be a bad practice?
No, in fact it's (more or less) required on any new columns added to an existing table to ensure backwards compat during migrations. More on reddit.com
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September 17, 2022Biztory
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.
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.
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
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.
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 - ... NULL values are some of the ... means nothing, and that’s exactly what NULL signifies – it’s a symbol to signify that no values exist in a column....
Database Journal
databasejournal.com › home › features
Working with NULL Values in SQL | DatabaseJournal.com | Database Journal
March 9, 2023 - In relational databases and RDBMS’, NULL values are a special value in SQL that are used to represent an unknown – or in some instances, a missing – value in a column or cell.
Khoury College of Computer Sciences
khoury.northeastern.edu › home › kenb › MeaningOfNull.html
The Meaning of Null in Databases and Programming Languages
The meaning of null in relational databases is a major source of confusion not only among database users but also among database textbook writers. 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.
Microsoft Learn
learn.microsoft.com › en-us › sql › connect › ado-net › sql › handle-null-values
Handling null values - ADO.NET Provider for SQL Server | Microsoft Learn
May 27, 2026 - 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 › 2076-some-disadvantages-of-allowing-null-values-in-relational-databases.html
Some Disadvantages of Allowing Null Values in Relational Databases
November 7, 2022 - As stated in that article, the value NULL has become a special marker to mean that no value exists. You could also say that NULL values may indicate that a column could have a value, but you don't know what that value should be yet.
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It's all about the context in which it's used. A null means there is no value but the reason for this will depend on the domain in which it is being used. In many cases the items you've listed are all valid uses of a null.
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It can mean any of those things (and it is not always obvious which), which is one argument against using nulls at all.
See: http://en.wikipedia.org/wiki/Null_(SQL)#Controversy
SQL Shack
sqlshack.com › working-with-sql-null-values
Working with SQL NULL values
May 19, 2021 - This article will explain what problems can occur when working with SQL NULL values and it also gives some solution recommendations to overcome these issues. In terms of the relational database model, a NULL value indicates an unknown 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. Consider this, lets say we have a database table called ‘PERSONS’ which contain of the following columns: ...
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Nulls are negatively viewed from the perspective of database normalization. The idea being that if a value can be nothing, then you really should split that out into another sparse table such that you don't require rows for items which have no value.
It's an effort to make sure all data is valid and valued.
In some cases having a null field is useful, though, especially when you want to avoid yet another join for performance reasons (although this shouldn't be an issue if the database engine is setup properly, except in extraordinary high performance scenarios.)
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One argument against nulls is that they don't have a well-defined interpretation. If a field is null, that could be interpreted as any of the following:
- The value is "Nothing" or "Empty set"
- There is no value that makes sense for that field.
- The value is unknown.
- The value hasn't been entered yet.
- The value is an empty string (for databases that don't distinguish between nulls and empty strings).
- Some application-specific meaning (e.g., "If the value is null, then use a default value.")
- An error has occurred, causing the field to have a null value when it really shouldn't.
Some schema designers demand that all values and data types should have well-defined interpretations, therefore nulls are bad.
Hyperskill
hyperskill.org › university › sql › sql-null-value
SQL NULL Value
October 2, 2024 - The SQL NULL value is a special marker in Structured Query Language (SQL) that represents missing or undefined data in a database. It can be applied to any data type, including numbers, strings, and dates.
Scaler
scaler.com › home › topics › sql › null value in sql
NULL Value in SQL - Scaler Topics
March 28, 2024 - NULL in SQL represents a column field in the table with no value. NULL is different from a zero value and from "none". NULL can be inserted in any column by using the assignment operator "=". Also, to test whether a NULL is present or not we have to use certain operators, for example, IS NULL ...
iNTERFACEWARE
help.interfaceware.com › v6 › dealing-with-null-data-from-databases
Dealing with NULL data from databases - iNTERFACEWARE Help Center
First: What NULL is supposed to mean from database theory, paraphased in plain(ish) english: NULL is often described as “UNKNOWN”, unfortunately this doesn’t really help to understand how it works · A better way to describe NULL is “not set yet”, or “not yet KNOWN”, this gives us some idea of the meaning · Another description is “any valid value”, we just don’t know which value yet (until it is entered in the future)