my $sql = "select MNref from comment_record where MNid=" . "\"$self->{_MNid}\"";
my $ccr = $dbh->prepare($sql);
$ccr->execute() or die "$!";

##</code><code>##

my $sql = "select MNref from comment_record where MNid= ?";
my $ccr = $dbh->prepare($sql);
$ccr->execute($self->{_MNid}) or die $ccr->errstr;