'Re: [freetds] How does FreeTDS support bulk export'

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List:       freetds
Subject:    Re: [freetds] How does FreeTDS support bulk export
From:       Johnny Yan <jyan () tableau ! com>
Date:       2016-08-16 20:14:15
Message-ID: DM5PR03MB273203DE2A0CDD4653893A38C3130 () DM5PR03MB2732 ! namprd03 ! prod ! outlook ! com
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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@lists.ibiblio.org] On Behalf Of Thompson, \
                William
Sent: Wednesday, August 10, 2016 5:37 AM
To: FreeTDS Development Group <freetds@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@lists.ibiblio.org] On Behalf Of Johnny Yan
Sent: 09 August 2016 23:29
To: freetds@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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