To the point guide to PL/SQL

PL/SQL constant holds a declared value and cannot change it in the program. The declaration of constant has its data type, name and value.

Syntax of Constant Declaration:

Constant_name CONSTANT datatype[Size] := Value; 

Here are some important details for above syntax

• Constant_name: The constant name.
• CONSTANT: is a keyword.
• Data type: PL/SQL data type.
• Size: size to store the maximum size value.
• Value: User must initialize the variable value. User cannot re-assign/change it.

Example:

In this example Stud_name is constant variable where its value cannot alter.

DECLARE
	Stud_num(3) := 8
	Stud_name CONSTANT varchar2(25) := 'Suman';
 BEGIN
	dbms_output.put_line(' Student number is: ' || Stud_num );
	dbms_output.put_line('Declared Constant:');
	dbms_output.put_line(' Student name is: ' || Stud_name);	
END;
/

Result: 

Student number is: 8
Declared Constant:
Student name is: Suman
PL/SQL procedure successfully operation.

The PL/SQL Literals

A literal is same as a constant and an explicit value like numeric, string, character, and boolean which are not represented by identifier. Literals are usually case sensitive.

• Numeric Literals
  
  This literal can be used in arithmetic expressions
  
  Example:
  number1 := 3.125346e3;  -- numeric literal
number2 := -7300.00;  -- numeric literal 

• Character Literals
  
  These literals include all the characters which are printable in the set like numbers, letters, spaces, and symbols.
  
  Example:
  'A' '%' '9' ' ' 'z' '('
  name1 VARCHAR2(1) := 'n'; -- character literal 

• String Literals
  
  This literal is a sequence of zero or group of characters enclosed by single quotes, like
  'Oracle’, '$13,00,000', '1-MAY-15' 

• BOOLEAN Literals
  
  This literal values are the predefined:
  TRUE, FALSE, and NULL. 

• Date and Time Literals
  
  It have various date formats like 1-MAY-15' or '1-MAY-15 01:14:06 AM'.
  
  

Example

DECLARE  
  msg1   VARCHAR2(1000);
  BEGIN
  msg1 := 'I am learning PL/SQL!!!';
 END;
/

Result

'I am learning PL/SQL!!!
PL/SQL procedure successfully completed.

In next part of this guide we will quickly familiarize ourselves with PL/SQL Operators