Oracle Database Discussions

Question regarding size allocation that occurs for NVARCHAR columns in sql server to NVARCHAR2 in Oracle in the migration tool.

The migration tool has converted NVARCHAR columns to be twice their size as NVARCH2 in Oracle. Example, a table whose column is mycol NVARCHAR(40) gets migrated as mycol NVARCHAR2(80).

In SQL Server land, the designation of a column as NVARCHAR(40) will physically store the column as 80 bytes. However, as I understand from this excerpt (taken from here: http://www.oracle.com/technology/oramag/oracle/03-nov/o63tech_glob.html), that Oracle in essence will do the same thing for NVARCHAR2:

To make it easy to allocate proper storage for Unicode values, Oracle9i Database introduced character semantics. You can now use a declaration such as VARCHAR2(3 CHAR), and Oracle will set aside the correct number of bytes to accommodate three characters in the underlying character set. In the case of AL32UTF8, Oracle will allocate 12 bytes, because the maximum length of a UTF-8 character encoding is four bytes (3 characters * 4 bytes/character = 12 bytes). On the other hand, if you're using AL16UTF16, in which case your declaration would be NVARCHAR2(3), Oracle allocates just six bytes (3 characters * 2 bytes/character = 6 bytes). One difference worth noting is that for UTF-8, a declaration using character semantics allows enough room for surrogate characters, whereas for UTF-16 that is not the case. A declaration such as NVARCHAR2(3) provides room for three UTF-16 code units, but a single supplementary character may consume two of those code units.

As I read this, NVARCHAR(40) in sql server should be equivalent to NVARCHAR2(40) in Oracle and not NVARCHAR2(80) as it gets translated to - am I missing something? We have a rather large database to migrate so I need to get this size allocation right (and I obviously don't want to truncate any data).

Thanks -