Whenever you declare a variable, PL/SQL assigns it a default value of NULL. If you want to initialize a variable with a value other than the NULL value, you can do so during the declaration, using either of the following:
- The DEFAULT keyword
- The assignment operator
For example:
counter binary_integer := 0;
greetings varchar2(20) DEFAULT 'Have a Good Day';
You can also specify that a variable should not have a NULL value using the NOT NULL constraint. If you use the NOT NULL constraint, you must explicitly assign an initial value for that variable. For example:
name VARCHAR(25) NOT NULL := 'Smith';
It is a good programming practice to initialize variables properly otherwise, sometimes program would produce unexpected result.