[freetds] unicode

James K. Lowden jklowden at freetds.org
Tue Jul 22 16:01:54 EDT 2008

Jason Young (Morgon) wrote:
> SQL Server is a pain in regards to sending UTF strings, as you'll need 
> to prefix all of your quoted strings with capital N, for example:
> INSERT INTO utf8_table (utf8string) VALUES (N'???')

I don't see what difference the 'N' prefix makes.  


	"Unicode strings have a format similar to character strings but are
preceded by an N identifier (N stands for National Language in the SQL-92
standard). The N prefix must be uppercase. For example, 'Michél' is a
character constant while N'Michél' is a Unicode constant. Unicode
constants are interpreted as Unicode data, and are not evaluated by using
a code page."

Remember that Win32 clients use USC-2.  The SQL text is sent to the server
as USC-2.  That is, the server sees 18 bytes:

$ iconv -f iso8859-1 -t ucs-2 | hexdump -C 
00000000  4e 00 27 00 4d 00 69 00  63 00 68 00 e9 00 6c 00 
00000010  27 00

No UTF-8 anywhere in sight.  

I don't know how to interepret Microsoft's statement though.  *All* SQL
text is transmitted as UCS-2.  When that 'e9 00' arrives, the server knows
it's UCS-2, regardless of whether the string is preceded by a 'N' or not. 
Once the constants are parsed out, each one has to be converted to the
column's encoding, based on its "collation" (unless it's a UCS-2 column,
of course).  So I don't see any "interpretation" happening based on the
'N' prefix.  

FreeTDS of course has to convert from the client's encoding to UCS-2.  It
will do so regardless of the data; the 'N' prefix means nothing to
FreeTDS.  The result is precisely as above: the data arrive as UCS-2, and
I see no effect of using the 'N' prefix or not.  


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