NULL Condition in SQL

1. IS NULL
2. IS NOT NULL

NOTES:

• The NULL conditions includes the IS NULL condition and IS NOT NULL conditions.
• The IS NULL conditions tests for nulls.
• A null value means the value is unavailable, unassigned, unknown or inapplicable. (null and zero both are different)
• Therefore, you cannot test with = because a null cannot be equal or unequal to any value.

Example:

The above example retrieves the last names and managers of all employees who do not have a manager.

Example:
To retrieve the names, salary of employees who don't receive commission we can write the query like:

Example:

The above example shows the name,sal and commission of employees who commission is not null, i.e.

the employee receives commission, it may be zero but not null.

So, remember: null and zero both are different.