A constant is defined as that holds a value that is once declared, and does not change in the program. Its declaration specified its name, data type, and its value and also allocates storage for it. This declaration can also be imposed on the NOT NULL constraint.
Declaring the constant.
It is declared by using the CONSTANT keyword. That requires an initial value and also does not allow that the value to be changed. See the example given below:
PI CONSTANT NUMBER := 3.141592654;
DECLARE
-- constant declaration
pi constant number := 3.141592654;
-- other declarations
radius number (5,2);
diameter number (5,2);
area number (10,2)
BEGIN
-- processing
radius := 9;
diameter := radius*2;
area := pi*radius*radius;
-- output
dbms_output.put_line(‘’Radius : ‘ || radius);
dbms_output.put_line(‘’Diameter : ‘ || diameter);
dbms_output.put_line(‘’Area : ‘ || area);
END;
/When we execute the above code, we get following result;
Radius: 9;
Diameter: 18;
Area: 254.4690049
PL/SQL procedure successfully completed.
