Although it is not required, it is generally a good idea to initialize a variable when creating it.
When variables are created, they can be assigned a value using the assignment operator, :=, or the DEFAULT keyword. Oracle suggests
that you use DEFAULT for variables that have a typical value and the assignment operator for variables that do not. A declaration can also specify a NOT NULL constraint, to prevent the assignment of
a NULL value to the variable. Variables that are not initialized have the value NULL. As with SQL, literal character data is always enclosed in single quotes. Similarly, quoted strings may not contain line breaks.
Variables can also be assigned values after declaration, in the executable section. This is typically done in one of two ways, using the assignment operator (:=)
or a SELECT INTO statement.
Once you have declared a variable and assigned it a value, you can display its assigned value in the context of PL/SQL using
the DBMS_OUTPUT.PUT_LINE stored procedure.
As is the case with most languages, special care must be taken when dealing with NULL values. For example, a variable can be assigned
the value of NULL + 1. The resulting assignment sets the variable to NULL, which might not be the intent.
At times you may want to utilize a special character in a character string such as a tab or a newline.
The CHR function can be used to insert these types of special characters.