W3Schools
w3schools.com › sql › sql_null_values.asp
SQL NULL Values - IS NULL and IS NOT NULL
SQL Examples SQL Editor SQL Quiz SQL Exercises SQL Server SQL Syllabus SQL Study Plan SQL Bootcamp SQL Certificate SQL Training ... If a field in a table is optional, it is possible to insert or update a record without adding any value to this field...
special marker and keyword in SQL indicating that something has no value
Factsheet
Null (SQL)
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Null (SQL)
Notation ω
Wikipedia
en.wikipedia.org › wiki › Null_(SQL)
Null (SQL) - Wikipedia
3 weeks ago - The NULL literal is untyped in SQL, meaning that it is not designated as an integer, character, or any other specific data type. Because of this, it is sometimes mandatory (or desirable) to explicitly convert Nulls to a specific data type.
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
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 is the meaning of ISNULL AND COALESCE in simple terms?
IS NULL means “when the field is blank”. Null is the absence of data. A space is not null. Any character is not null. If there is any data in the field than it is not null. Coalesce is like a hierarchy of fields: imagine you have phone numbers for contacts but you want the single most important phone number. Cell is better than work phone. Work phone is better than fax right? So if you coalesce: cell, phone, (in that order) you get the single most important number per person. Ie: if cell is null then gimme the work number, else gimme the fax so that HOPEFULLY, I have a number. And if I have a number, it is the most important. More on reddit.com
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August 16, 2022What is mean by ON DELETE [CASCADE | SET NULL]?
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September 7, 2019Videos
04:46
Understanding NULL Values in SQL | What NULL Means and How to Use ...
06:54
SQL Tutorial #17 - SQL IS NULL and IS NOT NULL | SQL NULL Values ...
17:05
SQL NULL vs Empty String vs Blank Space (Visually Explained) | ...
07:01
SQL | Null Function in SQL | ISNULL | COALESCE | IFNULL | NVL - ...
02:16
SQL - NULL Values - W3Schools.com - YouTube
Understanding Nulls in SQL
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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.
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
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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.
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
Null values generally indicate data that is unknown, not applicable, or to be added later. For example, a customer's middle initial might not be known at the time the customer places an order.
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.
ThoughtSpot
thoughtspot.com › sql-tutorial › sql-is-null
SQL IS NULL: Find Missing or Empty Values
March 12, 2026 - IS NULL is a logical operator in SQL that allows you to exclude rows with missing data from your results. Some tables contain null values—cells with no data in them at all. This can be confusing for heavy Excel users, because the difference ...
LearnSQL.com
learnsql.com › blog › what-is-null-in-sql
What Is a NULL in SQL? | LearnSQL.com
March 17, 2021 - Simply put, an SQL NULL means that we don’t have a value for that particular field. Maybe we don’t know what the value will be and we need a placeholder, like when an order has been shipped to a customer but not delivered yet; in that case, the delivery date will be NULL until the order has arrived.
Enki
enki.com › post › understanding-null-values-in-sql
Enki | Blog - Understanding NULL Values in SQL
NULL in SQL is a special marker used to indicate that a data value does not exist in the database.
GeeksforGeeks
geeksforgeeks.org › sql › sql-null-values
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.
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
Modern SQL
modern-sql.com › concept › null
Modern SQL: NULL — purpose, comparisons, NULL in expressions, mapping to/from NULL
“Every [SQL] data type includes a special value, called the null value,”0 “that is used to indicate the absence of any data value”.1 · The null value does not indicate why a value is absent—it simply marks the places that do not have ...
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.
MSSQLTips
mssqltips.com › home › sql null meaning and how to handle null values
SQL NULL Meaning and How to Handle NULL Values
June 20, 2024 - Jason could have a wallet but he left it at home. In that case, there is something in his wallet, we just don’t know what it is. We see this a lot with middle names/initials. NULL doesn’t mean the person doesn’t have a middle name, they probably just didn’t provide it, thus it is unknown.
Essential SQL
essentialsql.com › home › 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!
Vettabase
vettabase.com › what-does-null-mean-in-sql
What does NULL mean in SQL? - Vettabase
December 6, 2024 - But this is illogical: it should return all rows instead (which is usually what the SQL user expects). Why? Because phone must be equal to itself, it doesn’t matter if the value is unknown, or even missing. Aggregate functions are those that accept any number of 1-column rows and return exactly one value. COUNT(*) returns the number of rows. If a row only contains NULLs, it still counts as one. So, in this context, NULL is considered as an unknown existing value. COUNT(column) ignores NULLs. This means that, in this context, NULL is considered as a missing value.
Tsql
tsql.nu › t-sql-code › what-is-null
What is NULL? – tsql.nu
October 31, 2019 - Many Words. “Too long, didn’t read” might be your reaction, but just remember this one thing: To a person, NULL would mean either MISSING or UNKNOWN. To SQL, it always means UNKNOWN.
Biztory
biztory.com › blog › 2019 › 07 › 22 › 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.
DbSchema
dbschema.com › blog › tutorials › 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.
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....