On Mon, May 13, 2002 at 01:57:01AM -0700, Michael Peppler wrote:
> On Sun, 2002-05-12 at 13:11, Tim Bunce wrote:
> > [I've come back to look at this thread that I filed a while ago...]
> >
> > On Wed, Feb 13, 2002 at 01:04:15PM -0800, Michael Peppler wrote:
> > > Hi,
> > >
> > > The DBI docs state the following:
>
> <snip>
>
> > > However this syntax does NOT work with DBD::Sybase because of the way
> > > OpenClient handles the prepare. The issue is the "? is null" part:
> > > neither the Sybase client libs, nor the server can determine what
> > > datatype the placeholder is supposed to be, and I see no way to add a
> > > directive to tell the server that this item is of the same type as
> > > "product_code".
> >
> > Why do you have to?
>
> The problem is that a "prepared" statement with ?-style placeholders is
> sent as-is to the server, which compiles it, and generates the
> appropriate temporary stored procedure for it.
>
> The (? is null) bit generates the following error message from Sybase:
>
> ct_result(ct_dynamic(CS_PREPARE)) returned -205 at
> /usr/lib/perl5/site_perl/5.6.0/i386-linux/DBD/Sybase.pm line 105.
> DBD::Sybase::db prepare failed: Server message number=12828 severity=16
> state=1 line=1 server=troll procedure=DBD2 text=The datatype of a
> parameter marker used in the dynamic prepare statement could not be
> resolved.
>
> During the prepare() call Sybase will resolve all the input parameters,
> and determine the datatypes for each of them. But in the case of the (?
> is null) construct the '?' does not resolve to an existing column, so
> Sybase errors out.
Wow. Pity.
> > Are there any other valid sql statements that have this problem?
> > (Like using placeholders as parameters for functions that take
> > different kind of datatypes.)
>
> I don't know - I just tried the following:
> $dbh->prepare("select convert(varchar, ?, 109)");
> which promptly failed with
> The untyped variable ? is allowed only in in a WHERE clause or the SET
> clause of an UPDATE statement or the VALUES list of an INSERT statement.
>
> In this case the convert() call would be expecting a DATETIME
> column/variable.
> I tried this also with
> select sin(?)
> which clearly expects a float variable, and that fails with the same
> error.
>
> I don't know if this sort of prepare() would be valid with Oracle (or
> any other db engine), but it is definitely a no-no with Sybase.
Oracle would be fine with it. You get to bind the placeholder with
any type you like. You get a error when you execute the statement if
the bound type isn't valid, or can't be converted into something valid.
> > What wording have you added to the docs? [I'm trying to work out
> > what to say in the DBI docs.]
>
> Looks like I haven't done this yet.
>
> I'll try to formulate something in the next few days - I'll let you
> know.
Thanks.
Tim.
