W3Schools
w3schools.com › sql › sql_null_values.asp
SQL NULL Values - IS NULL and 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:
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.
SQL's NULL values are confusing – understanding how they work
A tricky one that catches me from time to time is the effect of a null in a subquery that you're doing "not in" operator on:
select a.* from A a where a.f1 not in (select b.f2 from B b where ...)
If the query for B produces any nulls, you'll always get no results from the query for A, regardless of the other content in A and B. That's because the query engine can't be sure any particular value is not in the list, because any null in the subquery is treated like an unknown that could stand for anything. So it returns null or false at each check of the not-in condition, and a null final result in a where clause won't have a record making it into the results, only positively true values would.
More on reddit.com 5
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June 19, 2017Replace nulls values in sql using select statement in mysql? - Stack Overflow
Ho to do this? What query can be written by using select statement where all nulls should be replaced with 123? I know we can do this y using, update tablename set fieldname = "123" where fie... More on stackoverflow.com
What is the best way to handle null in the aggregation function with the calculations?
Tip: You can use ISNULL(total_installment_amount,0) instead of that CASE statement for the sum aggregation I'm not quite sure what you mean for percentage calculation though. Are you trying to count records for a calculation? More on reddit.com
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July 5, 2021why am I having null in a sum in SQL?
Try this to ensure that the values are at least 0: COALESCE(column1,0) + COALESCE(column2,0) AS sum More on reddit.com
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August 16, 2023Videos
04:46
Understanding NULL Values in SQL | What NULL Means and How to Use ...
12:19
Learn about NULL values in SQL - learn SQL pt 8 - YouTube
08:29
SQL to find NULL in any column - YouTube
03:25
Handling Missing Values in SQL: Using IS NULL and IS NOT NULL - ...
00:42
Master NULL Values Fast: Explained in Under 1 Minutes! - YouTube
11:40
How To Handle NULL Values In MS SQL Server? - YouTube
Metaplane
metaplane.dev › blog › best-ways-to-handle-null-values-in-sql
The 5 best ways to handle NULL values in SQL | Metaplane
They check each product's `reorder_point` value. Any time they encounter a NULL (meaning no reorder point has been set), they automatically substitute 10 as a safe default threshold. Remember that `ISNULL` and `IFNULL`aren't universally supported.
Enki
enki.com › post › understanding-null-values-in-sql
Enki | Blog - Understanding NULL Values in SQL
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. Proper handling of NULL values is crucial when performing various database operations such as comparisons, sorting, and aggregations.
W3Schools
w3schools.com › sql › sql_isnull.asp
W3Schools.com
The "InOrder" column is optional, and may contain NULL values. ... Note: In the SQL above, if any of the "InOrder" values are NULL, the result will be NULL!
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.
Medium
medium.com › @riat06 › behaviour-of-null-values-in-sql-48c18564c46
Behaviour of NULL values in SQL. How does null value affects different… | by Ria Thomas | Medium
August 30, 2024 - The behaviour of NULL is same for all of these functions except COUNT() and GROUP BY(). For the SQL aggregate functions, NULL values are not considered while the operation is performed i.e if AVG() is used on a set of values which have NULL as well average is calculated by ignoring it from the calculation. To show an example, I have a sample table here with a few values in MySQL.
Reddit
reddit.com › r › programming › comments › 6i6xfu › sqls_null_values_are_confusing_understanding_how
r/programming - SQL's NULL values are confusing – understanding how they work
June 19, 2017 - In a lot of cases we don't want the semantic meaning that NULL has, but we need to mark a field missing a value. Unfortunately, the only option for numeric, date and timestamp fields tends to be the NULL value rather than some more proper MISSING 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 ...
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
Dataengineerthings
blog.dataengineerthings.org › demystify-null-values-in-sql-bc7e7e1b913a
Demystify NULL Values in SQL
March 4, 2020 - Things learned in our data engineering journey and ideas on data and engineering.
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.
Top answer 1 of 5
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You have a lot of options for substituting NULL values in MySQL:
CASE
select case
when fieldname is null then '123'
else fieldname end as fieldname
from tablename
COALESCE
select coalesce(fieldname, '123') as fieldname
from tablename
IFNULL
select ifnull(fieldname, '123') as fieldname
from tablename
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There is a statement called IFNULL, which takes all the input values and returns the first non NULL value.
example:
select IFNULL(column, 1) FROM table;
http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html#function_ifnull
W3Schools
w3schools.com › mysql › mysql_null_values.asp
MySQL NULL Values - IS NULL and 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:
DbSchema
dbschema.com › blog › tutorials › sql null values – is null, coalesce, nullif, and common pitfalls | dbschema
SQL NULL Values – IS NULL, COALESCE, NULLIF, and Common Pitfalls | DbSchema
August 22, 2023 - A SQL NULL value represents missing or unknown data — it is not zero, not an empty string, and not false. NULL is a special marker that means "no value exists here." Understanding NULL is essential because it affects filtering, aggregation, ...
Regenerativetoday
regenerativetoday.com › handling-null-values-in-sql
Handling NULL values in SQL – Regenerative
August 19, 2019 - So to deal with NULL, we can use IS NULL or IS NOT NULL to check if there is a null value. Here is an example of IS NULL. Following query statement in the picture below querying for the rows where price column has null values from the fun table of inventory database.
Database Journal
databasejournal.com › home › features
Working with NULL Values in SQL | DatabaseJournal.com
March 9, 2023 - In relational databases and RDBMS’, NULL values are a special value in SQL that are used to represent an unknown – or in some instances, a missing – value in a column or cell.
Atlassian
atlassian.com › data › databases › how to alter a column from null to not null in sql server
How to alter a column from NULL to NOT NULL in SQL server
Once the alteration to your column is made, it is a good practice to verify the column no longer allows any NULL values by running a simple INSERT test and trying to insert a new record with the NULL value in the altered column: 1INSERT INTO 2 clients(name, email, phone) 3VALUES 4 ('John Doe', 'jdoe@domain.com', NULL); If all went according to plan, SQL Server will issue an error stating that the column doesn’t allow NULL values:
Wikipedia
en.wikipedia.org › wiki › Null_(SQL)
Null (SQL) - Wikipedia
1 day ago - In a database table, the column reporting this answer would start with no value (marked by null), and it would not be updated with the value zero until it is ascertained that Adam owns no books. In SQL, null is a marker, not a value.
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
DB Vis
dbvis.com › thetable › dealing-with-null-in-sql-complete-guide
Dealing With NULL in SQL: Complete Guide
April 9, 2025 - In SQL, NULL represents missing or unknown values in a database table. Unlike zero or an empty string, NULL signifies the absence of a value–not zero, not an empty string, but a true unknown or undefined value.