PL/SQL - Constants and Literals

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In this chapter, we will discuss constants and literals in PL/SQL. 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 the 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, 'howcodex' 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.

S.No Literal Type & Example
1

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
2

Character Literals

'A' '%' '9' ' ' 'z' '('
3

String Literals

'Hello, world!'

'Howcodex'

'19-NOV-12'
4

BOOLEAN Literals

TRUE, FALSE, and NULL.
5

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 in the following program −

DECLARE 
   message  varchar2(30):= 'That''s howcodex.com!'; 
BEGIN 
   dbms_output.put_line(message); 
END; 
/

When the above code is executed at the SQL prompt, it produces the following result −

That's howcodex.com!  

PL/SQL procedure successfully completed.
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