http://www.dbonline.cn/source/oracle/20041023/PLSQL_use%20compose%20and%20unistr.htm
http://www.cnoug.org/archive/index.php/t-43401.html
http://searchdatabase.techtarget.com.cn/searchdatabase/504969415343734784/20050126/1905909_1.shtml
http://blog.itpub.net/post/468/9287
You can create a table using the NVARCHAR2 and NCHAR datatypes. The column length specified for the NCHAR and NVARCHAR2 columns is always the number of characters instead of the number of bytes:
对于非nchar或者nvarchar的类型,The column length 应该是the number of bytes
http://www.oracle.com.cn/onlinedoc/server.920/a96529/ch6.htm#1011079