CHAR « PL SQL Data Types « Oracle PL/SQL Tutorial

21.2.2.CHAR type variable
21.2.3.Compare CHAR and VARVHAR32 variables for equality
21.2.4.Constants are compared using blank-padded comparison semantics, so the trailing spaces won't affect the result.
21.2.5.Fixed length strings are compared with blank-padded comparison semantic
21.2.6.Compare fixed length string and a literal
21.2.7.Compare char against varchar, and the trailing spaces do matter.
21.2.8.Assigning an empty string to the character variable is exactly the same as assigning NULL to it.