High score system from my iphone game - php

Question

I have this loop in PHP to select all my scores from my game from a MySQL table.
My query is:
$sql = "SELECT * FROM $table WHERE ";
switch($type) {
case "global":
$sql .= "1 ";
break;
case "device":
$sql .= "udid = '$udid' ";
break;
case "name":
$sql .= "name = '$name' ";
break;
}
$sql .= "ORDER BY $sort ";
$sql .= "LIMIT $offset,$count ";
$result = mysql_query($sql,$conn);
The udid is a unique identifier. And the loop:
while ($row = mysql_fetch_object($result)) {
echo '<tr>
<td>
'.$rank.'
</td>
<td>
'.$row->name.'
</td>
<td>
'.$row->score.'
</td>
<td>
'.$row->udid.'
</td>
</tr>';
$rank++;
}
My question is simple, so a person can see inside the game at which rank he is.
"How to select a rank from a udid, outside of the loop".
Perhaps making a new query which selects the rank from a udid, or set up a variable from in the loop?

Answer 1

Here's how to query the database for the rank for player udid 1:
SELECT COUNT(*) AS rank
FROM tablename
WHERE score > (SELECT score FROM tablename WHERE udid = 1)
I'm assuming a higher score is better and you're only storing the highest score for each player.
With an index on score and udid, this should be pretty speedy.
What the query does is count the number of users who have a greater score than the selected user.
If a lower score is better, simply change it to this:
SELECT COUNT(*) AS rank
FROM tablename
WHERE score < (SELECT score FROM tablename WHERE udid = 1)
Which counts the number of players with a lower score.
Read all about MySQL indexes.

Answer 2

One option is writing a function that calculate the user's rank based on all the other's scores and returning it.
Then , calling it when the user wants to see his rank.
As far as I know , MMORPG games (for instance) have a rank field in their DB for each
player and they use a daily or hourly cron-job to update that rank.
So instead of running the 'calculate-the-rank' function each and every time a player
just want to see his rank, you'll just need to fetch the value of the field.
EDIT: code for the function (don't forget to add the rank field to your DB table)
File:
cronjob_update_rank.php:
require 'config.php'; //Or whatever contains your config and DB connection.
$rank = 1; //The best player ranked as 1
$getMembers = mysql_query("SELECT id FROM members ORDER BY `score` DESC");
while($mem = mysql_fetch_array($getMembers))
{
mysql_query("UPDATE members SET rank='$rank' WHERE id='{$mem['id']}'");
$rank++;
}
Please notice , it's just a sample code , you'll need to customize it for your needs.
Use your server panel to create a daily cronjob on that file.
(or ask for your hosting provider support with it).