rtrim returns char, with all the rightmost characters that appear in set removed; set default is a single blank. If char is a character literal, then you must enclose it in single quotes. rtrim works similarly to ltrim.
Both char and set can be any of the datatypes CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB. The string returned is of VARCHAR2 datatype and is in the same character set as char.