W3Schools
w3schools.com › sql › sql_notnull.asp
SQL NOT NULL Constraint
This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field. By default, a column can hold NULL values.
W3Schools
w3schools.com › sql › sql_null_values.asp
SQL NULL Values - IS NULL and IS NOT NULL
SELECT column_names FROM table_name WHERE column_name IS NOT NULL; Below is a selection from the Customers table used in the examples: The IS NULL operator is used to test for empty values (NULL values). The following SQL lists all customers with a NULL value in the "Address" field:
Videos
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W3Schools
w3schools.com › sql › sql_ref_not_null.asp
SQL NOT NULL
String Functions: Asc Chr Concat ... SQL Bootcamp SQL Certificate SQL Training ... The NOT NULL constraint enforces a column to not accept NULL values, which means that you cannot insert or update a record without adding a value ...
W3Schools
w3schools.com › mysql › mysql_null_values.asp
MySQL NULL Values - IS NULL and IS NOT NULL
The IS NOT NULL operator is used to test for non-empty values (NOT NULL values). The following SQL lists all customers with a value in the "Address" field:
W3Schools
w3schools.com › mysql › mysql_notnull.asp
MySQL NOT NULL Constraint
The NOT NULL constraint enforces a column to NOT accept NULL values. This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.
W3Schools
w3schools.com › mySQl › sql_ref_not_null.asp
SQL NOT NULL Keyword
The NOT NULL constraint enforces a column to not accept NULL values, which means that you cannot insert or update a record without adding a value to this field. The following SQL ensures that the "ID", "LastName", and "FirstName" columns will ...
W3Schools
w3schools.com › sql › sql_ref_is_not_null.asp
SQL IS NOT NULL
String Functions: Asc Chr Concat ... SQL Bootcamp SQL Certificate SQL Training ... The IS NOT NULL command is used to test for non-empty values (NOT NULL values)....
W3Schools
www-db.deis.unibo.it › courses › TW › DOCS › w3schools › sql › sql_null_values.asp.html
SQL NULL Values - IS NULL and IS NOT NULL
SQL Functions SQL Avg() SQL Count() SQL First() SQL Last() SQL Max() SQL Min() SQL Sum() SQL Group By SQL Having SQL Ucase() SQL Lcase() SQL Mid() SQL Len() SQL Round() SQL Now() SQL Format() SQL Quick Ref SQL Hosting ... NULL values represent missing unknown data.
Mimo
mimo.org › glossary › sql › is-not-null
SQL IS NOT NULL Condition: Syntax, Usage, and Examples
# SQL IS NOT NULL: Syntax, Usage, and Examples The `SQL IS NOT NULL` condition checks whether a column contains a value rather than being empty. In SQL, a `NULL` represents missing or undefined data—not the number zero, an empty string, or false. Use `IS NOT NULL` to return rows where values ...
W3Schools
w3schools.com › sql › sql_isnull.asp
SQL COALESCE(), IFNULL(), ISNULL(), NVL() Functions
The COALESCE() function returns the first non-NULL value in a list of values. The COALESCE() function works in MySQL, SQL Server, and Oracle (not in MS Access).
GeeksforGeeks
geeksforgeeks.org › sql › sql-not-null-constraint
SQL NOT NULL Constraint - GeeksforGeeks
February 10, 2026 - In SQL, NOT NULL constraint in SQL ensures a column must always contain a value and cannot be left empty.
Programiz
programiz.com › sql › is-null-not-null
SQL IS NULL and IS NOT NULL (With Examples)
IS NULL and NOT NULL in SQL are used to check if any field contains null values. In this tutorial, you will learn about the SQL IS NULL and NOT NULL with the help of examples.
Tutorialspoint
tutorialspoint.com › sql › sql-null-values.htm
SQL - NULL Values
Here, NOT NULL signifies that column should always accept an explicit value of the given data type. You can insert NULL values into the columns where we did not use NOT NULL. Let us create a table with the name CUSTOMERS in the SQL database ...
DB Vis
dbvis.com › thetable › sql-is-not-null-condition-definitive-guide
SQL IS NOT NULL Condition: Definitive Guide
August 13, 2025 - This checks whether the SQL expression (a column, hardcoded value, or other type of expression) is a NULL value. If the value of the expression holds NULL, the condition returns false. If it does not hold NULL, it returns true.
Hightouch
hightouch.com › sql-dictionary › sql-not-null
SQL NOT NULL - Syntax, Use Cases, and Examples | Hightouch
December 29, 2023 - A NOT NULL constraint in SQL is a database constraint that ensures a column must always contain a value. It prohibits the insertion of NULL values, making it mandatory for every row to have a non-null value in the specified column.
Hightouch
hightouch.com › sql-dictionary › sql-is-not-null
SQL IS NOT NULL - Syntax, Use Cases, and Examples | Hightouch
December 29, 2023 - The SQL IS NOT NULL operator is used to filter rows in a database table where a specified column's value is not NULL. It is the opposite of the IS NULL operator.
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.
Reddit
reddit.com › r/sql › need some knowledge on null and not null
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
Top answer 1 of 5
8
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
2 of 5
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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.
Wikipedia
en.wikipedia.org › wiki › Null_(SQL)
Null (SQL) - Wikipedia
3 weeks ago - The 1986 SQL standard basically adopted Codd's proposal after an implementation prototype in IBM System R. Although Don Chamberlin recognized nulls (alongside duplicate rows) as one of the most controversial features of SQL, he defended the design of Nulls in SQL invoking the pragmatic arguments that it was the least expensive form of system support for missing information, saving the programmer from many duplicative application-level checks (see semipredicate problem) while at the same time providing the database designer with the option not to use Nulls if they so desire; for example, to avoid well-known anomalies (discussed in the semantics section of this article).
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
Top answer 1 of 5
12
If you need to represent unknown data in a column, you make it nullable. If you will always have data in the column, it's better to make it not nullable, as
- Dealing with nulls can be annoying and counterintuitive
- It saves a bit of space
- On some database systems, null values are not indexed.
2 of 5
3
When a field is set to NOT NULL, it cannot be empty. Which means you have to specify a value for that field when inserting a record.