Standard SQL defines NCHAR or NATIONAL CHAR as a way to indicate that a CHAR column should use some predefined character set. MySQL 5.5 uses utf8 as this predefined character set. For example, these data type declarations are equivalent:

CHAR(10) CHARACTER SET utf8
NATIONAL CHARACTER(10)
NCHAR(10)

As are these:

VARCHAR(10) CHARACTER SET utf8
NATIONAL VARCHAR(10)
NCHAR VARCHAR(10)
NATIONAL CHARACTER VARYING(10)
NATIONAL CHAR VARYING(10)

You can use N'literal' (or n'literal') to create a string in the national character set. These statements are equivalent:

SELECT N'some text';
SELECT n'some text';
SELECT _utf8'some text';

For information on upgrading character sets to MySQL 5.5 from versions prior to 4.1, see the MySQL 3.23, 4.0, 4.1 Reference Manual.