The national character set is a shorthand notation that you can
    use for a character set of your choice. SQL uses the national
    character set for the following elements:

    o  For all columns and domains with the data type NCHAR or NCHAR
       VARYING and for the NCHAR data type in a CAST function. For
       information about these data types, see the Data_Types HELP
       topic.

    o  For all parameters in SQL module language with the data type
       NCHAR or NCHAR VARYING.

    o  For all character string literals qualified by the national
       character set; that is, the literal is preceded by the letter
       N and a single quotation mark (for example, N'). For more
       information, see the Literals HELP topic.

    You can specify the national character set at the session and
    database level. See the Oracle Rdb Introduction to SQL and the
    Oracle Rdb Guide to Database Design and Definition for more
    detail about session and database character sets.

    You specify the national character set for a database when you
    create the database. You cannot alter the national character set
    of a database.

    SQL uses DEC_MCS as the national character set, unless you have
    set the dialect to MIA or specified a national character set at
    the session level. You can override any national character set
    by specifying another national character set when creating a
    database.

    When you compile SQL programs (either SQL module language or
    precompiled SQL), SQL uses the following to derive the national
    character set:

    o  The NATIONAL CHARACTER SET clause in the DECLARE ALIAS
       statement specifies the national character set of the alias
       at compile time. It controls the national character set for
       column and domain definitions and the NCHAR and NCHAR VARYING
       data types in a CAST function. At run time, SQL uses the
       national character set of the attached database for these
       elements.

    o  The NATIONAL CHARACTER SET clause of the SQL module header
       and the DECLARE MODULE statement specifies the character set
       for literals qualified by the national character set and for
       parameters defined with the data type NCHAR or NCHAR VARYING.

    o  In dynamic SQL, the SET NATIONAL CHARACTER SET statement
       specifies, at run time, the character set for columns with
       the data type NCHAR and NCHAR VARYING and for character string
       literals qualified by the national character set.

    o  The RDB$CHARACTER_SET logical name. However, the logical name
       is deprecated and will not be supported in a future release.

                                   NOTE

       Although SQL does not require that the national character
       set of the database and the module match, Oracle Rdb
       recommends that you define both with the same character
       set.