Php sql, form resubmits on page load - php

Question

Neglecting the obvious security flaws of mysql and nor sql escape strings, does anybody know why my sql tables are getting filled up with empty msgs on page reload.
Every sinngle time the page reloads a form submits. I'm confused as to why this is happening, and how do i stop it?
<?php
ob_start();
session_start();
$con = mysql_connect("localhost","username","pass");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
$dates = date('Y-m-d H:i:s');
$uid = $_SESSION['user_id'];
$msg_id = (int) $_GET['msg_id'];
mysql_select_db("db_table", $con);
$result = mysql_query("SELECT users.first_name, users.last_name , intro.intro, intro.outro FROM intro INNER JOIN users ON intro.user_id = users.user_id WHERE intro.message_id = {$msg_id}");
while($row = mysql_fetch_array($result))
{
echo "<div id=\"start\"><div class=\"namedate\"><h1>". $row['first_name'] ." ". $row['last_name'] . "</h1><h2>test</h2></div><div id=\"holdmsg\"><div class=\"cent\"><strong>" . $row['intro'] . "</strong><br><i>" . $row['outro'] ."</i></div></div></div> " ;
}
PART RELEVANT TO THE FORM is this part and also the $_GET, at the top of the page.
<form action="" method="post">
<?php
$sql="INSERT INTO messages (user_id, intro_id , msg, date ) VALUES (('$uid'), {$msg_id} ,'$_POST[msg]', ('$dates'))";
if (!mysql_query($sql,$con))
{
die('Error: ' . mysql_error());
}
mysql_close($con);
?>
<textarea rows="2"style="float:left" name="msg" type="text"placeholder="Elaborate on your idea..."></textarea>
<input id="togz2" style="float:right; "type="submit" value="SUBMIT" name="submit" class="butts">
</div></div>
</form>

Answer 1

Why not do it like this?
if (mysql_query($sql,$con))
{
header('location:yourpage.php');
}else{
die('Error: ' . mysql_error());
}
Also I dont see any such statement above your insert query
Like
if(isset($_REQUEST['submit'])){ //to check if posted
$sql="INSERT ......
}
Beside that you should also validate your data before inserting into a database.

Answer 2

Here is good example how to prevent duplicate entry on page load
Please refer link http://www.webhostingtalk.com/showthread.php?t=700175.
<?php
session_start();
$faction = $_REQUEST['faction'] ;
if (!is_array($_SESSION['serials'])) $_SESSION['serials'] = array ();
if ($_REQUEST['serial']){
if ( in_array ($_REQUEST['serial'] , $_SESSION['serials'] ) ){
// duplicate submition, nullify it
$faction = '';
}else{
$_SESSION['serials'][] = $_REQUEST['serial'] ;
}
}
if ($faction) { // form submited
// if faction is not set completely ignore submition
}
?>
<form>
<input type="hidden" name="faction" value="42">
<input type="hidden" name="serial" value="<?=rand(1000000 , 9999999)?;>">
....
the rest of the form is here
....
</form>
Another Solution:-
You should re-direct to a new page after successful insertion.