Defining a Null Value

Null Value :

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

Example :

• postgres=# select ename, sal, comm from emp;

ename | sal | comm
--------+---------+---------
SMITH | 800.00 |
ALLEN | 1600.00 | 300.00
WARD | 1250.00 | 500.00
JONES | 2975.00 |
MARTIN | 1250.00 | 1400.00
BLAKE | 2850.00 |
CLARK | 2450.00 |