What is a NULL Value in SQL?

A null value signifies the absence of data or an unknown value. It is distinct from zero, an empty string, or any other placeholder that may represent a value. In essence, a null value indicates that no information has been provided for that particular field. How to test for NULL values? In conclusion, it is important to remember that null values cannot be tested using standard comparison operators due to their unique nature in SQL. Instead, using the IS NULL and IS NOT NULL operators provides a reliable means to identify and handle null values in database queries, enabling better data management and analysis. IS NULL operator The IS NULL operator in SQL is used to test for null values in a database. It checks whether a specified field or expression is null (i.e., has no value) and returns true if it is. Conversely, the IS NOT NULL operator checks if a field contains a value, returning true if the field is not null.
Code

SELECT * FROM sales 
WHERE PhoneNumber IS NULL;

IS NOT NULL operator
The IS NOT NULL operator in SQL is used to test whether a specified field or expression contains a value (i.e., it is not null). This operator is essential for filtering records in a database where you want to ensure that certain fields have been populated.

Code

SELECT * FROM sales 
WHERE PhoneNumber IS NOT NULL;