Null value is an 'unknown' value in SQL Server. If a column has null value, It means that the data is either missing or unknown.

The Null Value

The 'Null" value is different from an empty value(' '). An empty value cannot be considered as a NULL. Since 'Null' is unknown, any operation with null value will also return a null value. Also Null is not equal to Null. Since the default option for a column is null, you have to explicitly state that a column is not null when creating a table. To Handle a null situation we use the following functions.

• ISNull Function
• Coalesce Function

INull function is covered in the next chapter and Coalesce is covered here.

The Create Table example with default null option

In the above columns, it can be seen that DesignationID, PhoneNo and salary columns are optional columns. That means that they can contain null values. So when the query is run on the 'Employees' table, it returns the rows of records as shown below along with the null values that have not been entered.

The below query displays all the columns and data from the 'EMPLOYEES' table.