sql injection through address bar.

[harmor19]

Thank you.

This is offtopic
I have four button "up, down, right, left"
When a button is pressed it adds or substracts from the value and re-inserts into the database.

PHP Code:

if (isset($_POST['up']))
    {
      $move_v = $rpg['move_v'] + 10;
    }
    elseif (isset($_POST['down']))
    {
       $move_v = $rpg['move_v'] - 10; 
    }  
    else
   {    
      $move_v = $rpg['move_v'];   
    }
      //code for left and right buttons here ($move_h)

$query = "UPDATE rpg_character 
     SET 
     move_v = '$move_v', 
     move_h ='$move_h'
     WHERE characterid='".$rpg['characterid']."'";
     mysql_query($query); 


What I'm doing is using the php image function and on that script I'm getting the vertical ($move_h) and the horizontal ($move_h) positions.
It'll place and image according to those coordinates.

So my question is if I have a lot of people playing at the same time will it bog down the server?