FreeTDS Development Group

["Lowden, James K" <LowdenJK AT bernstein.com>]

> From: Rogers, Tom [mailto:tom.rogers AT ccur.com]
> Sent: July 1, 2003 9:04 AM
> To: 'FreeTDS Development Group'
> Subject: RE: [freetds] Using sp_executesql with Microsoft SQL Server
> 2000
> 
> Up until about a month ago, we were told by several on this group that
> FreeTDS would not support output parameters on MS SQL because 
> of a change
> Microsoft made in the way it handled output params, circa SQL 
> 7.0, SPx.  At
> that time, they changed the output params such that they were 
> being sent
> "out of band" and not part of the normal messages returned 
> (or something like that).

Let me try to clarify that.  :-)

Nick Castellano discovered that as of SQL Server 7.0 SP3, using TDS 7.0,
Microsoft stopped supporting output parameters embedded in SQL text.  If you
sent

        declare @a int
        exec a @a output

prior to SP3, the server sent a special result set packet.  With db-lib, the
application would call dbnumrets() and friends to fetch the output.
Starting with SP3, Microsoft simply ceased sending that special result set
packet; the same application would be told there were no output parameters
returned.  

The remedy lay in the RPC protocol, which Frediano had begun to work on for
a different purpose,  for placeholder support.  In short order we were able
to add the db-lib and ct-lib RPC functions.   If they're used, the server
will once again return the data.  There are unit tests for both:

src/ctlib/unittests/rpc_ct_param.c
src/ctlib/unittests/rpc_ct_setparam.c
src/dblib/unittests/rpc.c
src/dblib/unittests/t0022.c

Microsoft's own db-lib uses TDS 4.2, which is unaffected.  I'm not familiar
enough with the ODBC idiom to know whether or not it has any non-RPC way to
retrieve output parameter values.  Perhaps the change affected no Microsoft
customers.  

> query = "{? = call mysp(?, ?, ?}"

>From reading the ChangeLog, I doubt you can fetch output parameters that way
yet, but it looks close.  

--jkl
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