IS NULL

Check for NULL (empty) values

Syntax
      expression IS NULL;

Key
   Expression can be a column_name or a calculated value.

Examples

Return all the receipts where the delivery date is null.

SQL> select * from receipts
where delivery_date IS NULL;

Return all the addresses where the zip code is null (we do not have their zip code)

SQL> select * from addresses
where zip_code IS NULL;

“Using dummy values to represent NULL or unknown is usually a bad idea, in 1979 a Los Angeles man named Robert Barbour found this out the hard way when he sent an application to the California Department of Motor Vehicles (DMV) requesting personalized license plates for his car”

Related

Oracle SQL Functions
IS NOT NULL - Check for items that contain a value
ORA-00932 inconsistent datatypes