Re: What SQL type for SQLBindParameter for NVARCHAR(MAX)/NTEXT when using UTF-8 locale?

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<[email protected]>:
>> 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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