标准 SQL 定义了 NCHAR 或 NATIONAL CHAR 作为指示 CHAR 列应使用某个预定义字符集的方式。MySQL 使用 utf8 作为该预定义字符集。例如，这些数据类型声明是等效的：Standard SQL defines NCHAR or NATIONAL CHAR as a way to indicate that a CHAR column should use some predefined character set. MySQL 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)

像这些一样：As are these:

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

您可以使用 N'literal'（或 n'literal'）来创建国家字符集中的字符串。这些语句是等价的：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';

MySQL 8.4 将国家字符集解释为 utf8mb3，该字符集现在已被弃用。因此，使用 NATIONAL CHARACTER 或其同义词之一来定义数据库、表或列的字符集时，会出现类似如下的警告：MySQL 8.4 interprets the national character set as utf8mb3, which is now deprecated. Thus, using NATIONAL CHARACTER or one of its synonyms to define the character set for a database, table, or column raises a warning similar to this one:

NATIONAL/NCHAR/NVARCHAR implies the character set UTF8MB3, which will be
replaced by UTF8MB4 in a future release. Please consider using CHAR(x) CHARACTER
SET UTF8MB4 in order to be unambiguous.