The SQL IS NULL test whether the user-specified expression is empty or not, and if it is, TRUE will return. Otherwise, it returns FALSE. The basic syntax of this IS NULL is
SELECT Column_Names FROM Table WHERE Expression IS NULL
Simple SQL IS NULL Example
For this SQL Server IS NULL demonstration, We are going to use the [TenCustomers] table, and the data inside the table is

In this example, we use this function to return all the records whose Last Name is a empty value
SELECT [CustomerKey] ,[FirstName] ,[LastName] ,[EmailAddress] ,[YearlyIncome] ,[EnglishOccupation] ,[AddressLine1] ,[Phone] FROM [TenCustomers] WHERE [LastName] IS NULL

Example 2
The below image shows the data inside the SQL Server Emp table, and it has 15 records.

The following query returns all the employee records whose Office Phone numbers are empty values
SELECT [Id] ,[Name] ,[Education] ,[Occupation] ,[YearlyIncome] ,[Office Phone] ,[Mobile] ,[Home Phone] FROM [Emp] WHERE [Office Phone] IS NULL

It returns the employees whose Office Phone, and Mobile numbers are empty.
SELECT [Id] ,[Name] ,[Education] ,[Occupation] ,[YearlyIncome] ,[Office Phone] ,[Mobile] ,[Home Phone] FROM [Emp] WHERE [Office Phone] IS NULL AND [Mobile] IS NULL
