W3Schools
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SQL NULL Values - IS NULL and IS NOT NULL
A NULL value represents an unknown, missing, or inapplicable data in a database field.
Microsoft Learn
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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).
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, 2022Why 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, 2022Videos
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
1 day 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
Essential SQL
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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!
Tutorialspoint
tutorialspoint.com โบ sql โบ 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
Biztory
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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.
GeeksforGeeks
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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.
Navicat
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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.
DB Vis
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Working with NULL in Databases: Turn Frustration Into Delight
July 5, 2024 - ... NULL values are some of the ... means nothing, and thatโs exactly what NULL signifies โ itโs a symbol to signify that no values exist in a column....
Database Journal
databasejournal.com โบ home โบ features
Working with NULL Values in SQL | DatabaseJournal.com
March 9, 2023 - In relational databases and RDBMSโ, NULL values are a special value in SQL that are used to represent an unknown โ or in some instances, a missing โ value in a column or cell.
Microsoft Learn
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Handling null values - ADO.NET Provider for SQL Server | Microsoft Learn
June 25, 2024 - 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).
Top answer 1 of 16
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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.
Databasedesign-resource
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NULL values in a database: A programmer's nightmare
Should we be able to store NULL values in a database. A discussion of NULL values with examples
SQL Shack
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Working with SQL NULL values
May 19, 2021 - This article will explain what problems can occur when working with SQL NULL values โโand 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 โบ 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.
Hyperskill
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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.
DbSchema
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SQL NULL Values โ IS NULL, COALESCE, NULLIF, and Common Pitfalls | DbSchema
August 22, 2023 - SQL NULL values are one of the most nuanced parts of the language. They require special operators (IS NULL, IS NOT NULL), explicit handling in aggregates, and careful design decisions when building schemas. Use COALESCE to substitute defaults, NULLIF to prevent division-by-zero errors, and always test nullable column behavior in JOIN and WHERE conditions before deploying to production. Connect DbSchema to your database to audit NULL columns visually, run targeted queries, and model nullable relationships clearly for your entire team.
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 - This query gets the employee ID and the first non-NULL value among WorkPhoneNumber and PersonalPhoneNumber. The NULLIF function returns NULL if the two specified expressions are equal. If they are not equal, it returns the first expression. ... This query returns the Id and the Price, but if the Price is 0, it returns NULL instead. In this guide, you saw what NULL means in SQL Server and what operators and functions the database offers to deal with it.
Oracle
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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.
Oracle
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Nulls
November 12, 2025 - 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. Oracle Database treats a character value with a length of zero as null.