PL/SQL Constants

                                                       PL/SQL-Constants

A constant holds a value that once declared, does not change in the program. A constant declaration specifies its name, data type, and value, and
allocates storage for it. The declaration can also impose the NOT NULL constraint.

Declaring a Constant
A constant is declared using the CONSTANT keyword. It requires an initial value and does not allow that value to be changed. For example:

PI CONSTANT NUMBER := 3.141592654;
DECLARE
   -- constant declaration
   pi constant number := 3.141592654;
   -- other declarations
   radius number(5,2);
   dia number(5,2);
   circumference number(7, 2);
   area number (10, 2);
BEGIN
   -- processing
   radius := 9.5;
   dia := radius * 2;
   circumference := 2.0 * pi * radius;
   area := pi * radius * radius;
   -- output
   dbms_output.put_line('Radius: ' || radius);
   dbms_output.put_line('Diameter: ' || dia);
   dbms_output.put_line('Circumference: ' || circumference);
   dbms_output.put_line('Area: ' || area);
END;
/
When the above code is executed at SQL prompt, it produces the following result:

Radius: 9.5
Diameter: 19
Circumference: 59.69
Area: 283.53

Pl/SQL procedure successfully completed.
The PL/SQL Literals
A literal is an explicit numeric, character, string, or Boolean value not represented by an identifier. For example, TRUE, 786, NULL, 'tutorialspoint' are all literals of type Boolean, number, or string. PL/SQL, literals are case-sensitive. PL/SQL supports the following kinds of literals:

Numeric Literals

Character Literals

String Literals

BOOLEAN Literals

Date and Time Literals

The following table provides examples from all these categories of literal values.

Literal Type Example:
Numeric Literals
050 78 -14 0 +32767

6.6667 0.0 -12.0 3.14159 +7800.00

6E5 1.0E-8 3.14159e0 -1E38 -9.5e-3

Character Literals 'A' '%' '9' ' ' 'z' '('
String Literals
'Hello, world!'

'Tutorials Point'

'19-NOV-12'

BOOLEAN Literals TRUE, FALSE, and NULL.
Date and Time Literals DATE '1978-12-25';
TIMESTAMP '2012-10-29 12:01:01';
To embed single quotes within a string literal, place two single quotes next to each other as shown below:

DECLARE
 message  varchar2(30):= 'That''s tutorialspoint.com!';
BEGIN
 dbms_output.put_line(message);
END;
/
When the above code is executed at SQL prompt, it produces the following result:

That's tutorialspoint.com!

PL/SQL procedure successfully completed.