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  • From: Sebastien FLAESCH <sf AT 4js.com>
  • To: FreeTDS Development Group <freetds AT lists.ibiblio.org>
  • Subject: Re: [freetds] What SQL type for SQLBindParameter for NVARCHAR(MAX)/NTEXT when using UTF-8 locale?
  • Date: Fri, 19 Oct 2012 10:23:48 +0200

Hello Frediano,

Summary: Issue fixed when using SQL_WLONGVARCHAR.

More comments inlined.

On 10/18/2012 09:54 PM, Frediano Ziglio wrote:
2012/10/18 Sebastien FLAESCH<sf AT 4js.com>:
Hello,

I am using a UTF-8 encoding in my Linux FreeTDS client program,
and want to insert LOB data into NVARCHAR(MAX)/NTEXT columns.

For now, I bind the SQL Parameter with:

ctype = SQL_C_CHAR;
sqltype = SQL_LONGVARCHAR;
precision = 0x10000000;

This works find as long as the data is ASCII (and probably also
ISO-885901), but when using UTF-8 sequences, I get this error:

SQL State: HY000
SQL code : 2402
[FreeTDS][SQL Server]Error converting characters into server's character set.
Some character(s) could not be converted


Mmm... probably the encoding used by ODBC is not what you expected.
Try setting the ClientCharset attribute.

I was already using ClientCharset=UTF-8 in the ODBC data source.

I guess this is expected, because I use SQL_LONGVARCHAR...


Yes, longvarchar should be fine. I think FreeTDS should be smart
enough to use NVARCHAR(MAX) from protocol 7.2.

I don't think so:

I am using now SQL_WLONGVARCHAR,
I have FreeTDS 0.92 installed.
I have TDS_Version=8.0 set in the ODBC data source.
But in the SQL Server Profiler, I see an N'@P1 NTEXT' parameter for
sp_prepexec.


For NCHAR/NVARCHAR types, I use SQL_WCHAR / SQL_WVARCHAR SQL types
to bind my UTF-8 buffers, and this works fine.

But for large objects, what SQL type should I use?

I tried with SQL_WVARCHAR and a large size, without success:

[FreeTDS][SQL Server]Invalid string or buffer length


The encoding should be in SQLWCHAR with size in bytes usually (so
multiple of sizeof(SQLWCHAR)) and probably you still want the long
version (SQL_WLONGVARCHAR).

How to specify the precision for a CLOB?

As a comparison, with Easysoft SQL Server ODBC driver, you can bind
UTF-8 buffers with:

ctype = SQL_C_CHAR;
sqltype = SQL_WVARCHAR;
precision = SQL_SS_LENGTH_UNLIMITED;


I wasn't even aware of this constant!
I don't understand why this extension is necessary...

I think SQL_SS_LENGTH_UNLIMITED makes sense:

By design, unlike [N]CHAR(x) or [N]VARCHAR(x) types, a LOB type has
no size (it has a maximum size regarding storage limits).

There are other SQL Server specific defines in sqlncli.h such as:

SQL_SS_TIME2_STRUCT

Thanks for reading, please let me know what I should use!

Seb

Frediano
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