DBI cursor behaviour with multiple statements?

Paul Boddie paul at boddie.net
Thu Oct 10 12:26:31 CEST 2002

Henrik.Weber at sys.aok.de (Henrik Weber) wrote in message news:<7e964d1d.0210090210.724589c5 at posting.google.com>...
> In the last few days I have made some experiments with ADO and the Jet
> OLE DB provider. They seem to understand several syntax styles for
> parameters more or less directly. For the rest I think it is possible
> to reformat the query string. Alright, I'll make the paramstyle user
> configurable.

It was just a suggestion, but the pyformat paramstyle is misleading,
in my opinion, and should not have been proposed by the DB-API


> No reason to apologise. Basically I was under that illusion. I hadn't
> given much thought to parameters when I posted my first message. Well,
> I got answers for two questions by posting only one. That's pretty
> efficient ;-)

Usually I give no answers and people somehow work it out by
themselves, so you've made me work harder than usual. ;-)

> >   SELECT * FROM table WHERE column IN :1
> Would you also expect the database module to know to place parentheses
> around the placeholder? The Jet Provider complains about them missing,
> so the user at least has to write:
> SELECT * FROM table WHERE column IN (:1)

That's an interesting point, but it could well be an artifact of the
SQL parser used in the Jet stuff. I would expect parentheses to be
used to indicate an expression or a sequence, where the sequence would
possibly have more than one comma-separated value. Perhaps, the Jet
implementation specifically treats the content of the parentheses as a
sequence in this particular case, but the binding mechanism only
supports single values. There are certainly many possible
explanations, but only one of them is correct. ;-)

> The Jet OLE DB provider does not like lists or tuples as parameters
> directly. What might work is to try to bind the parameter. When the
> attempt fails determine if the parameter is a sequence and if so
> replace the placeholder with a number of new placeholders depending on
> the length of the sequence. Then the elements of the sequence could be
> bound one by one to the new placeholders.

Yes, this would be a good fallback technique that could be useful in
other database modules, too. (Weak hint to other module maintainers!)

> Thanks for your input. It will help me address some issues I'm just
> now starting to come across.

I've never actually written a proper database module, but I have
modified and debugged one or two, and I did once start an iODBC
wrapper. In these days of Pyrex, it's tempting to give it another shot
instead of using SWIG. Still, it's good that you find this discussion


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