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. Answer from belkarbitterleaf on reddit.com
W3Schools
w3schools.com › sql › sql_null_values.asp
SQL NULL Values - IS NULL and IS NOT NULL
String Functions: Asc Chr Concat ... Plan SQL Bootcamp SQL Certificate SQL Training ... A field with a NULL value is a field with no value....
Hightouch
hightouch.com › sql-dictionary › sql-is-null
SQL IS NULL - Syntax, Use Cases, and Examples | Hightouch
December 29, 2023 - The SQL IS NULL operator is used to filter rows where a specified column's value is NULL. A NULL value in a database represents the absence of data, and the IS NULL operator is used to identify and select rows that contain NULL values in a ...
What 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 is NULL in SQL? - Stack Overflow
I am confuse about what is the value of NULL in SQL. NULL I think is empty. So will it contain any garbage value or unknown value or like 0 in integer or blank in character? 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 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, 2022Videos
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How to handle NULL in SQL - YouTube
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How to use the SQL IS NULL Condition - YouTube
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SQL query to check IS Null and IS not Null data - YouTube
DB Vis
dbvis.com › thetable › the-definitive-guide-to-the-null-sql-server-value
The Definitive Guide to the NULL SQL Server Value
September 12, 2024 - Read this article to ensure that your knowledge of NULL values is not null! 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.
Reddit
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?
Top answer 1 of 5
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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.
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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.
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 in a data field.
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.
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 -
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
Top answer 1 of 5
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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.
W3Schools
w3schools.com › sql › func_sqlserver_isnull.asp
SQL Server ISNULL() Function
The ISNULL() function returns a specified value if the expression is NULL. If the expression is NOT NULL, this function returns the expression. ... If you want to use W3Schools services as an educational institution, team or enterprise, send ...
Wikipedia
en.wikipedia.org › wiki › Null_(SQL)
Null (SQL) - Wikipedia
1 week 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 ...
Microsoft Learn
learn.microsoft.com › en-us › sql › t-sql › queries › is-null-transact-sql
IS NULL (Transact-SQL) - SQL Server | Microsoft Learn
3 weeks ago - To determine whether an expression is NULL, use IS NULL or IS NOT NULL instead of comparison operators (such as = or !=). Comparison operators return UNKNOWN when either or both arguments are NULL. 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.
Coginiti
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 ...
Oracle
docs.oracle.com › en › database › oracle › oracle-database › 26 › sqlrf › Nulls.html
SQL Language Reference
1 month ago - If a column in a row has no value, then the column is said to be null, or to contain null. Nulls can appear in columns of any data type that are not restricted by NOT NULL or PRIMARY KEY integrity constraints.
Mimo
mimo.org › glossary › sql › is-null
SQL IS NULL Condition: Syntax, Usage, and Examples
The SQL IS NULL condition helps you check if a column contains no value, meaning it's undefined or missing. In relational databases, NULL represents the absence of data, not zero or an empty string.
GeeksforGeeks
geeksforgeeks.org › sql › sql-null-values
NULL values in SQL - GeeksforGeeks
July 23, 2025 - In SQL, some records in a table may not have values for every field, and such fields are termed as NULL values. These occur when data is unavailable during entry or when the attribute does not apply to a specific record.
W3Schools
w3schools.com › sql › sql_ref_is_null.asp
SQL IS NULL
String Functions: Asc Chr Concat ... SQL Bootcamp SQL Certificate SQL Training ... The IS NULL command is used to test for empty values (NULL values)....
Quora
quora.com › What-is-the-significance-of-NULL-in-SQL
What is the significance of NULL in SQL? - Quora
Answer (1 of 11): I concur with Greg with the (widely accepted) opinion that Codd's original concept of NULL (3-state logics) was pregnant with many [I mean MANY] bugs in many [I mean MOST] applications. However, I still believe that the original idea of data with special-value was not that bad....
Medium
medium.com › @tw4512 › working-with-null-in-sql-a-beginners-guide-12-6a1a6948c622
Working with Null in SQL: A Beginner’s Guide(12) | by Tamanna shaikh | Medium
February 16, 2024 - They represent the absence or unknown of any data in a column. In this blog post, we will learn how to handle null values in SQL queries using various techniques and functions. This is part of our SQL Learning series, where we cover the basics ...
ThoughtSpot
thoughtspot.com › sql-tutorial › sql-is-null
SQL IS NULL | Basic SQL | ThoughtSpot
3 weeks ago - Starting here? This lesson is part of a full-length tutorial in using SQL for Data Analysis. Check out the beginning. ... IS NULL is a logical operator in SQL that allows you to exclude rows with missing data from your results.
W3Schools
w3schools.com › sql › sql_isnull.asp
W3Schools.com
SQL Examples SQL Editor SQL Quiz SQL Exercises SQL Server SQL Syllabus SQL Study Plan SQL Bootcamp SQL Certificate SQL Training ... Suppose that the "UnitsOnOrder" column is optional, and may contain NULL values. ... In the example above, if any of the "UnitsOnOrder" values are NULL, the result will be NULL.