NUll Value: According to ORACLE Null is a value which is not known, not defined, not predictable, inapplicable.

You have data in the tables which may be null. In the employees table if you select commission_pct you will see many rows with null values. Oracle has beautiful approaches to handle null values. As a programmer I try to utilise all the null related things to avoid confusion. Also i want you to know that null is neither equal to a blank space nor its a zero value. Always imagine infinity when you think of null, when you add something to infinity, its infinity, similarly when you add something to null its null.

Null defined by ORACLE:

• A null is a value that is unavailable, unassigned, unknown, or inapplicable.
• A null is not the same as zero or a blank space.

Please follow the query and note the results for your practise which results in null vaues.

• select null+100, null*100,null/12,null-100 from dual