CREATE TABLE t1(a NVARCHAR(10))
This is for compatibility with MSSQL, DB2, Informix and some other DBMSs.

Note, standard SQL doesn't have "NVARCHAR" syntax.
There are only these syntaxes in SQL2003:
 NATIONAL VARCHAR
 NCHAR VARCHAR
 NATIONAL CHARACTER VARYING 
 NCHAR VARYING

- Tests were added for all the above syntaxes.