the syntax

select ? from ... where ..
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isn't valid SQL.

Are you sure? Any links to documents that specify that?

At least SQLite accepts it:

#!/usr/bin/perl

use strict;
use warnings;
use DBI;

my $dbh=DBI->connect('dbi:SQLite:dbname=/tmp/foo.sqlite','','',{ Raise
+Error => 1 });
my $sth=$dbh->prepare('select ? as answer');
$sth->execute(42);
$sth->dump_results();
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'42'
1 rows
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PostgreSQL can't determinate the column type without a little help, but accepts it with type information. SQLite has a very relaxed relation to data types, so it is no surprise that SQLite does NOT need help.

#!/usr/bin/perl

use strict;
use warnings;
use DBI qw( SQL_INTEGER );

my $dbh=DBI->connect('dbi:Pg:dbname=postgres','postgres','postgres',{ 
+RaiseError => 1 });
my $sth=$dbh->prepare('select ? as answer');
$sth->bind_param(1,42,SQL_INTEGER);
$sth->execute();
$sth->dump_results();
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42
1 rows
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Alexander