W3Schools
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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....
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
3 weeks 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
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
Need 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 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, 2022What type of integrity constraint is NOT NULL?
not null is simply part of data type definition it's same type of "constraint" as int or datetime More on reddit.com
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June 29, 2024Videos
05:55
How to Handle NULL Values in SQL Queries | Datamites - YouTube
04:46
Understanding NULL Values in SQL | What NULL Means and How to Use ...
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Learn about NULL values in SQL - learn SQL pt 8 - YouTube
04:27
Tutorial#27 How NULL value treated in Oracle SQL Database|IS NULL ...
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DBMS - Null Values in SQL - YouTube
Microsoft Learn
learn.microsoft.com โบ en-us โบ dotnet โบ framework โบ data โบ adonet โบ sql โบ 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).
GeeksforGeeks
geeksforgeeks.org โบ sql โบ 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....
Khoury College of Computer Sciences
khoury.northeastern.edu โบ home โบ kenb โบ 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.
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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.
Essential SQL
essentialsql.com โบ home โบ 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!
Biztory
biztory.com โบ blog โบ 2019 โบ 07 โบ 22 โบ null-values-tips
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.
Reddit
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r/SQL on Reddit: Need some knowledge on NULL and NOT NULL
December 22, 2021 -
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Where and why exactly a null is used?
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What is exactly null and not null? To my understanding Not null we use when its mandatory to insert some value in that field, also when we give check constraint so by default the column will be not null right?
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By adding new column through alter method default values are null, so how would I be able to insert values in it and is it right to give not null constraint to that new column while adding through alter method, basically when null and when not null to be used?...
god this is so confusing please help me, ik im asking alot but im really confused
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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
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Thoughts in this can vary but I'll give my input. NULL should be used where it is known that there can definitely be no value. If a person's record has an optional telephone number when signing up to a website, and they do not complete a number upon their submission, then a NULL is a valid value. However, if we are utilising something like "effective from" and "effective to" of a row of data, then effective to should never be NULL, we always determine that a row is either currently effective, or is historic and superceded. As a result, the "active" row should not hold a NULL in effective to, even though it is not known. It should be a future, default date, and the column should be set with a NOT NULL constraint.
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 ...
Navicat
navicat.com โบ en โบ company โบ aboutus โบ blog โบ 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.
LearnSQL.com
learnsql.com โบ blog โบ 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.
DbSchema
dbschema.com โบ blog โบ tutorials โบ sql null values explained with examples
SQL NULL Values Explained with Examples
August 22, 2023 - In SQL, NULL is a special marker used to indicate that a data value does not exist in the database. It is important to note that NULL is not the same as an empty string or a zero value.
Reddit
reddit.com โบ r/learnsql โบ 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?
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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.
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.
Oracle
docs.oracle.com โบ en โบ database โบ oracle โบ oracle-database โบ 26 โบ sqlrf โบ Nulls.html
Nulls
February 24, 2026 - 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.
Enki
enki.com โบ post โบ 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.
DB Vis
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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 ยท Now when any data is inserted into the column named column_1, the default โ โpre-builtโ if you will โ value will be NULL.
Microsoft Learn
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NULL and UNKNOWN (Transact-SQL) - SQL Server | Microsoft Learn
No two null values are equal. Comparisons between two null values, or between a null value and any other value, return unknown because the value of each NULL is unknown. Null values generally indicate data that is unknown, not applicable, or to be added later.