if the problem is only the assigning it's an example:
in mysql you can have this one:
create table store_list(id_markets int auto_increment,store_type int,primary
key(id_markets));
and for page this one:
<html>
<head>
<title>Store</title>
</head>
<form method="post">
<?php
$connection=Mysql_connect('localhost','admin','123');
Mysql_select_db('net',$connection);
if(array_key_exists('sub',$_POST))
if(isset($_POST['store_type']) )
{
$Type =$_POST['store_type'];
$ID=$_POST['id'];
$sql ="update store_list set store_type=$Type where id_markets=$ID";
$res = mysql_query($sql,$connection);
}
?>
<select name='store_type'>
<option value=0>store type<option>
<option value=1>corporate<option>
<option value=2>standard<option>
</select>
ID:<input type='text' name='id'>
<input type='submit' name='sub' value='update the type'>
</form>
</html>
also I didn't understand your code that you have 'id_store' and 'id_markets'
it's confusing for me
if it wasn't your problem please clarify your question maybe I can help.