FreeTDS Development Group

[Johnny Yan <jyan AT tableau.com>]

Hi Bill, 

So sorry about the delay. 

The "bulk export" is referred to insert multiple rows into a temp table which 
we just created. In terms of the ODBC API calls, the stack is roughly like 
this, 

SQLAllocHandle( SQL_HANDLE_STMT, ...) );
SQLExecDirectW(..., "CREATE TABLE [#temp_table_name] (columns)",...);

SQLAllocHandle( SQL_HANDLE_STMT, ... );
SQLPrepare(..., "INSERT INTO [#temp_table_name] (columns) VALUES (?,...) 
",...)
SQLSetStmtAttrW(..., SQL_ATTR_PARAMSET_SIZE, num_rows_export, SQL_IS_UINTEGER 
);
SQLBindParameter(..., SQL_PARAM_INPUT, ...)
SQLExecDirect(...,"INSERT INTO [#temp_table_name] (columns) VALUES (?,...) 
",...)

With MS Native Client on Windows and/or Simba driver on OSX, this is working 
just fine. But with FreeTDS, we found that the placeholds(?) in the prepared 
statement were replaced with the value of the params. I actually debugged a 
little bit of the FreeTDS code. In _SQLExecute(TDS_STMT * stmt):odbc.c(3270), 
it goes into the branch "else if (stmt->query)" and the following comments 
are confusing since we're passing in a prepared statement. Because of this, 
the code path then goes into tds_multiple_query -> tds_send_emulated_execute, 
which looks like really "emulating"(bulk export).

I suspect the "stmt->query" condition might be misleading in the first place 
but not sure at all. What do you think?

If you need more info, please let me know.

Thanks,
Johnny

-----Original Message-----
From: FreeTDS [mailto:freetds-bounces AT lists.ibiblio.org] On Behalf Of 
Thompson, William
Sent: Wednesday, August 10, 2016 5:37 AM
To: FreeTDS Development Group <freetds AT lists.ibiblio.org>
Subject: Re: [freetds] How does FreeTDS support bulk export

Hi Johnny,

What is this "bulk export" you refer to?
If there's INSERT statements going on, it sounds more like an import to me...
What is wrapped around FreeTDS in your application? 
I think it's more likely that it's this that is deciding on the approach of 
generating multiple INSERT statements, rather than FreeTDS.

Bill

-----Original Message-----
From: FreeTDS [mailto:freetds-bounces AT lists.ibiblio.org] On Behalf Of Johnny 
Yan
Sent: 09 August 2016 23:29
To: freetds AT lists.ibiblio.org
Subject: [freetds] How does FreeTDS support bulk export

Hi,

We've observed, through the freetds.log, that when we try to bulk export 
multiple rows, what FreeTDS really does is replacing the ? placehold with the 
corresponding param value(s), then concatenating multiple "INSERT INTO..." 
statements into a single query, and finally sent it through the wire. Is this 
what we're supposed to expect? How does FreeTDS support bulk export?

Thanks,
Johnny
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