For many databases placeholders aren't just a textual substitution. It needs a real column name there in order to compile it to whatever internal representation the handle has. You really need to consult the specific DBD::Foo and database documentation to tell what's alowable as a placeholder and what's not. What you might could do is to prepare a handle for each column you plan on using:

my %sth;
foreach( qw( guest name shoe_size ) ) {
  $sth{$_} = $dbh->prepare( qq{
SELECT distinct email from contacts where $_ = ? order by email
}) or warn "Error preparing for $_: " . $dbh->errstr . "\n";
}
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You could even build the handles dynamically on demand as they're needed.

$sth{$column} ||= $dbh->prepare( make_select( $column ) );
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