Re: Prepared Statements - Mailing list pgsql-jdbc

I believe the main problem is that we would simply break existing code. This is a serious issue! If this patch do get
applied,I'm a lucky person to read this list, because I can protect myself from problems in my system knowing about
this...but lots of people probably will have serious problems using this new driver versions... 

On Fri, 18 Jul 2003 16:22:39 -0400
Darin Ohashi <DOhashi@maplesoft.com> wrote:

> > I think yes.
> > Depends on your definiton of "in general", of course,
> > Where I come from, at least "in general", the
> > PreparedStatement should
> > be able to handle *everything* you can do with sql.
>
> Well, what I meant by "in general", is more along the lines of "is this
> behaviour covered by the spec".  Does the JDBC spec explicitly deny this kind of
> behaviour.
>
> My understanding, which might be wrong, is that "?" is a placeholder for a data
> value and not a placeholder for SQL syntax, so, for example I would never expect
> a PS would be able to do something like this:
>
> ps := c.prepareStatement( "??" );
> ps.setString( 1, "SELECT * " );
> ps.setString( 2, "FROM table" );
> ps.execute();
>
> The final SQL statement produced by a PS should be any valid SQL string, but a
> PS should not have to deal with being able to put that string together from
> arbitrary pieces of data.  I would be surprised if there was not a document
> somewhere that specified what is and is not valid to pass via a "?".
>
> Looking at this particular example, it looks to me (of course, I have a limited
> amount of SQL experience) that "(1,2,3,4)" contains syntax.  Using (?,?,?,?) the
> "?" replace data and that should work.  As "(1,2,3,4)" contains syntax, I don't
> think it is a valid thing to substitute in.
>
> > Depends on the implementation...
> > If the backend doesn't support it, the driver should take care of
> > working around that
> > (e.g. by switching to 'non-precompiled' version in this case)
> > until the
> > backend is able to support it (I don't see any reason why it
> > just cannot
> > be done theoretically).
>
> Well, if you allow syntax to be substituted in to the PS, then the backend can't
> precompile because it does not have a syntatically complete statement.  What you
> substitute in could completely change the query optimization.
>
> >
> > > Do other JDBC drivers support this kind of substitution?
> > >
> > Yes. They do (at least, the ones I worked with do).
>
> Do they use actual precompiled statements or just with string concats?
>
> >> I am not going to lose it :-)
> > Thanks to the driver being opensource I have control over what I am
> > going to lose :-)
>
> Lose it from the official driver.  You can, of course, do what ever you like
> with your personal version of the driver.
>
> >
> > >
> > >Instead of creating your own driver, why not just subclass
> > Statement into
> > >something that looks like a PreparedStatement but just glues
> > strings together?
> > >
> > Ummm... because it already exists? That's what postgres
> > PreparedStatement does (by default in 7.3, and always in previous
> > versions)...
>
> That is what it currently does, I don't think that is what it will do in the
> future when (if) it actually represents  a precompiled statement.
>
> > No, that's not what I want...
> > What I want is an abstraction of the implementation-specific details,
> > that lets me effectively execute sql queries.
> > If it can precompile my query, I want it to precompile it. If
> > it cannot,
> > I can live with that (for a while).
> > I just don't want to *know* what it is doing.
>
> I accept that, but then you have to be willing to live by the rules of the spec,
> and I suspect this behaviour violates the spec.
>
> Darin
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster


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