PL/SQL Constants

As the name implies a constant is a value used in a PL/SQL Block that remains unchanged throughout the program. A constant is a user-defined literal value. You can declare a constant and use it instead of actual value.

The Syntax to declare a constant is:

constant_name CONSTANT datatype := VALUE;

constant_name is the name of the constant i.e. similar to a variable name.The word CONSTANT is a reserved word and ensures that the value does not change.

VALUE - It is a value which must be assigned to a constant when it is declared. You cannot assign a value later.  For example, to declare salary_increase, you can write code as follows:

DECLARE

salary_increase CONSTANT number (3) := 10;

You must assign a value to a constant at the time you declare it. If you do not assign a value to a constant while declaring it and try to assign a value in the execution section, you will get an error. If you execute the below PL/SQL block you will get error.

DECLARE     

 salary_increase CONSTANT number(3):=100;

BEGIN

  dbms_output.put_line (salary_increase);

END;