$rs = mysql_query("Select id From TableName")
while($row = mysql_fetch_array($rs))
{
$id = $row["id"] //<-זה המשתנה של הID
$x = $id * 455;
mysql_query("Update tableName Set abc='".$x."' Where id='$id'")
}

$abc = array();
$result = mysql_query("SELECT id FROM my_table");
while ($row = mysql_fetch_array($result) {
    $abc[] = $row["id"];
}
foreach ($abc as $new_id) {
    $new_id = $new_id +15;
    $second_result = mysql_query("SELECT id FROM my_table WHERE id = '$new_id';
    if (mysql_num_rows($second_result) > 0) {
         echo "The New ID Exists";
    }else{
         echo "The New ID Dosn't Exists";
    }
}