Constants are compared using blank-padded comparison semantics : VARCHAR2 « PL SQL Data Types « Oracle PL/SQL Tutorial

SQL>
SQL> SET ECHO ON
SQL> SET SERVEROUTPUT ON
SQL> DECLARE
  2    fixed_length_10  CHAR(10);
  3    fixed_length_20  CHAR(20);
  4    var_length_10    VARCHAR2(10);
  5    var_length_20    VARCHAR2(20);
  6  BEGIN
  7    
  8    
  9    IF 'AAAA' = 'AAAA          ' THEN
 10      DBMS_OUTPUT.PUT_LINE
 11      ('Constant: ''AAAA'' = ''AAAA          ''');
 12    END IF;
 13
 14  END;
 15  /
Constant: 'AAAA' = 'AAAA          '

PL/SQL procedure successfully completed.

SQL>

21.4.VARCHAR2
	21.4.1.	VARCHAR2
	21.4.2.	VARCHAR2 type variable
	21.4.3.	varchar2 type with default value
	21.4.4.	Trim a text string in PL/SQL
	21.4.5.	Test the strings for equality
	21.4.6.	Using Single Quote Characters as Part of Text Strings
	21.4.7.	Represents the old way of placing quotes inside the text, namely to double them
	21.4.8.	Concatenate several string constants
	21.4.9.	Concatenate both string variables and constants
	21.4.10.	Concatenate two string variables
	21.4.11.	Comparison of CHAR with VARCHAR2.
	21.4.12.	When comparing CHAR strings against VARCHAR2 strings, use the rtrim function to eliminate trailing spaces
	21.4.13.	Constants are compared using blank-padded comparison semantics
	21.4.14.	Fixed length strings are also compared with blank-padded comparison semantic
	21.4.15.	Comparison of a fixed length string and a literal
	21.4.16.	Compare a variable length string against a fixed length, and the trailing spaces do matter.
	21.4.17.	The maximum lengths of varchar2 strings do not matter, only the assigned values
	21.4.18.	Demonstrates that empty strings are NULL