Perl DBI Sample with MySQL DDL

I've been experimenting with Perl and MySql and wrote this code for connecting and writing to a database:

#   MySQL DDL to create database used by code 
#
#   CREATE DATABASE sampledb;
#
#   USE sampledb;
#   
#   CREATE TABLE `dbtable` (
#     `id`  int(11) NOT NULL AUTO_INCREMENT,
#     `demo` longtext,
#     PRIMARY KEY  (`id`)
#   ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

# PERL MODULES
use strict;
use warnings;
use DBI; #http://dbi.perl.org

# CONFIG VARIABLES
my $platform = "mysql";
my $database = "sampledb";
my $host = "localhost";
my $port = "3306";
my $username = "root";
my $password = "password";

# DATA SOURCE NAME
my $dsn = "dbi:$platform:$database:$host:$port";

# PERL DBI CONNECT
my $connect = DBI->connect($dsn, $username, $password);

# VARS for Examples
my $query;
my $query_handle;
my $id;
my $demo;

# Example 1 using prepare() and execute() INSERT

    # SAMPLE VARIABLE AND VALUES TO PASS INTO SQL STATEMENT
    $id = 1;
    $demo = "test";

    # INSERT
    $query = "INSERT INTO dbtable (id, demo) VALUES ('$id', '$demo')";
    $query_handle = $connect->prepare($query);
    $query_handle->execute();
    undef $query;

# Example 2 using do() UPDATE   

    # SAMPLE VARIABLE AND VALUES TO PASS INTO SQL STATEMENT
    $id = 1;
    $demo = "test 2";

    # UPDATE
    $query = "UPDATE dbtable SET demo = '$demo' WHERE id = $id";
    $query_handle = $connect->do($query);
    undef $query;

Is this the correct/idiomatic way to access a database in Perl? Are there any other improvements I could make?

Couple of things I noticed:

When you connect to the database, you don't check that the connection succeeded. The most common way I've seen to do this in Perl is:

my $connect = DBI->connect($dsn, $username, $password)
   or die "Connection Error:  DBI::errstr\n";

If the connection fails, the program will then display the connection failure message so you can see what's going on.

I see that you use two different ways of accessing the database. It would be better to pick one and use it for all your inserts/updates unless there is a compelling reason not to - it keeps future readers from trying to figure out why you did it differently. In this case I'd reccomend using execute since it allows you to execute multiple times:

$query_handle = $connect->prepare("INSERT INTO dbtable (id, demo) VALUES (?, ?)");
$query_handle->execute($id, $demo);
$id = 2;
$demo = "test2";
$query_handle->execute($id, $demo);

Also don't forget to disconnect:

$connect->disconnect;

StackExchange Code Review Q#1465, answer score: 3