sub add_foo {
   my ($bar, $blah) = @_;
   
   my $sth = $dbh->prepare('INSERT INTO foo SET '
                            . "bar  = isnull(?, 'default_bar'), "
                            . "blah = isnull(?, 'default_blah')) "
        or die "Couldn't prepare statement: " . $dbh->errstr;

    $sth->execute($bar, $blah)
        or die "Couldn't execute statement: " . $sth->errstr;
    
    my $id = $dbh->last_insert_id(undef, undef, qw(foo id))
        or die "no insert id?";
    
    return $id;
}