to_single_byte returns char with all of its multibyte characters converted to their corresponding single-byte characters. char can be of datatype CHAR, VARCHAR2, NCHAR, or NVARCHAR2. The value returned is in the same datatype as char.
Any multibyte characters in char that have no single-byte equivalents appear in the output as multibyte characters. This function is useful only if your database character set contains both single-byte and multibyte characters.