将来自sql数据填充的列表的数据插入sql

Question

I want to insert into different sql table the data coming from list populated by data coming from sql table. Please help

   if(isset($_POST['submit'])){
     mysql_connect("localhost","root","") or die(mysql_error());
        mysql_select_db("edge");
        $sql = "INSERT INTO my_table (this_is_one)
                    VALUES ('".$_POST['this_is_one']."')";

    }

//Connect and select array to dropdown
$conn = mysql_connect("localhost","root","") or die(mysql_error());
        mysql_select_db("save");


$options = '';
$sql = "SELECT * FROM reg1"; 
$result = mysql_query($sql,$conn);

while($row = mysql_fetch_array($result)) {
    $options .="<option>" . $row['Last_Name'] . "</option>";
}

$menu="<form id='this_is_one' name='this_is_one' method='post' action='listpopulate.php'>
  <p><label>filter</label></p>
    <select name='this_is_one' id='this_is_one'>
      " . $options . "
    </select>
    <input type='submit' value='submit'>    
</form>";