w3schools.com › sql › sql_null_values.asp

SQL NULL Values - IS NULL and IS NOT NULL

It is not possible to test for NULL values with comparison operators, such as =, <, or <>. We will have to use the IS NULL and IS NOT NULL operators instead. SELECT column_names FROM table_name WHERE column_name IS 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:

Null

special marker and keyword in SQL indicating that something has no value

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 … Wikipedia

Factsheet

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Factsheet

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en.wikipedia.org › wiki › Null_(SQL)

Null (SQL) - Wikipedia

1 week ago - In SQL, NULL is a reserved word used to identify this marker. A null should not be confused with a value of 0. A null indicates a lack of a value, which is not the same as a zero value. For example, consider the question "How many books does Adam own?" The answer may be "zero" (we know that ...

Null propagation

Comparisons with NULL and the three-valued logic (3VL)

Analysis of SQL Null missing-value semantics

Check constraints and foreign keys

Aggregate functions

When two nulls are equal: grouping, sorting, and some set operations

Effect on index operation

Null-handling functions

Data typing of Null and Unknown

BOOLEAN data type

Further reading

Videos

SQL NULL vs Empty String vs Blank Space (Visually Explained) | ...

How to handle NULL in SQL - YouTube

SQL Tutorial #17 - SQL IS NULL and IS NOT NULL | SQL NULL Values ...

How to use the SQL IS NULL Condition - YouTube

SQL IS NULL and IS NOT NULL operator | Oracle SQL fundamentals ...

December 25, 2018

Tutorial#27 How NULL value treated in Oracle SQL Database|IS NULL ...

August 13, 2018

dbvis.com › thetable › the-definitive-guide-to-the-null-sql-server-value

The Definitive Guide to the NULL SQL Server Value

September 12, 2024 - In SQL Server, NULL indicates data that is unknown, not applicable, or yet to be provided. For example, assume a column for a middle name is nullable. In this case, NULL values indicate that the person either does not have a middle name or this ...

hightouch.com › sql-dictionary › sql-is-null

SQL IS NULL - Syntax, Use Cases, and Examples | Hightouch

December 29, 2023 - This is useful when you want to ... The syntax for using the IS NULL operator is as follows: SELECT columns FROM table_name WHERE column_name IS NULL; columns: The columns you want to retrieve in the query....

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 -

Where and why exactly a null is used?
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?
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

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

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.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 in a data field.

sqlshack.com › working-with-sql-null-values

Working with SQL NULL values

May 19, 2021 - For example, the following query will not return any rows. The reason for this issue is related to the structure of the SQL NULL because it does not specify an explicit value thus comparing an unknown value with an exact value result will be false. According to ANSI (American National Standard Institute) standards, any comparison or calculation performed with NULL values result must be NULL as we have just stated above.

stackoverflow.com › questions › 21987177 › what-is-null-in-sql

What is NULL in SQL? - Stack Overflow

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

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.

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coginiti.co › home › beginner › sql is null

What is the IS NULL Operator in SQL? - Coginiti

September 25, 2023 - A NULL value indicates that the data is missing or unknown, while a value of 0 indicates that the data is explicitly known and set to zero. If you are analyzing a stock table, the quantity of a product would be NULL when you don’t have the ...

learnsql.com › blog › what-is-null-in-sql

What Is a NULL in SQL? | LearnSQL.com

For example, if we want to delete all rows from our Springfield_Folks table that have a NULL value in Spouse_Name, we can execute this command: DELETE Springfield_Folks WHERE Spouse_Name IS NULL · At this point, it should be clear what SQL NULL means in the design and use of information stored in databases. Null elements are very useful for representing real-life situations where a piece of information is absent. But they should be used with ...

w3schools.com › mysql › mysql_null_values.asp

MySQL NULL Values - IS NULL and IS NOT NULL

It is not possible to test for NULL values with comparison operators, such as =, <, or <>. We will have to use the IS NULL and IS NOT NULL operators instead. SELECT column_names FROM table_name WHERE column_name IS NULL; SELECT column_names FROM table_name WHERE column_name IS NOT NULL; Below is a selection from the "Customers" table in the Northwind sample database: 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:

Microsoft Learn

learn.microsoft.com › en-us › sql › t-sql › queries › is-null-transact-sql

IS NULL (Transact-SQL) - SQL Server | Microsoft Learn

The code samples in this article use the AdventureWorks2025 or AdventureWorksDW2025 sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page. The following example returns the name and the weight for all products for which either the weight is less than 10 pounds, or the color is unknown, or NULL. SELECT Name, Weight, Color FROM Production.Product WHERE Weight < 10.00 OR Color IS NULL ORDER BY Name; GO · The following example returns the full names of all employees with middle initials.

modern-sql.com › concept › null

Modern SQL: NULL — purpose, comparisons, NULL in expressions, mapping to/from NULL

For example, the SQL language itself uses the null value for the absent values resulting from an outer join.2 Although exceptions exist,3 it is not generally possible to tell why a value is null.

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?

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.

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.

geeksforgeeks.org › sql › sql-null-values

NULL values in SQL - GeeksforGeeks

July 23, 2025 - The UPDATE query modifies the row where the SSN is NULL for the employee named Aditya Arpan, replacing it with a valid value · NULL values in SQL are essential for representing missing or inapplicable data. Understanding their behavior, impact on constraints, and three-valued logic is crucial for writing accurate queries.

thoughtspot.com › sql-tutorial › sql-is-null

SQL IS NULL | Basic SQL | ThoughtSpot

3 weeks ago - You can select rows that contain no data in a given column by using IS NULL. SELECT * FROM tutorial_billboard_top_100_year_end WHERE artist IS NULL OR TRIM(artist) = ''; WHERE artist = NULL will not work—you can't perform arithmetic on null values.

Microsoft Learn

learn.microsoft.com › en-us › sql › t-sql › language-elements › null-and-unknown-transact-sql

NULL and UNKNOWN (Transact-SQL) - SQL Server | Microsoft Learn

Applies to: SQL Server Azure SQL ... Warehouse in Microsoft Fabric SQL database in Microsoft Fabric · NULL indicates that the value is unknown....

w3schools.com › sql › sql_ref_is_null.asp

SQL Examples SQL Editor SQL Quiz SQL Exercises SQL Server SQL Syllabus SQL Study Plan SQL Bootcamp SQL Certificate SQL Training ... The IS NULL command is used to test for empty values (NULL values). The following SQL lists all customers with ...

programiz.com › sql › is-null-not-null

SQL IS NULL and IS NOT NULL (With Examples)

In SQL, the IS NULL condition is used to select rows if the specified field is NULL. It has the following syntax: SELECT column1, column2, ... FROM table WHERE column_name IS NULL; ... Here, the above SQL query retrieves all the rows from the Employee table where the value of the email column ...

w3schools.com › sql › sql_isnull.asp

SQL IFNULL(), ISNULL(), COALESCE(), and NVL() Functions

SQL Examples SQL Editor SQL Quiz ... and may contain NULL values. ... In the example above, if any of the "UnitsOnOrder" values are NULL, the result will be NULL....