php calculating top ten percent from database?

Question

I have this search running successfully that returns players skills and attributes. I want to get the top ten percent in particular columns. I was trying to use this:

$j=0;
while($percentile_row = mysql_fetch_array($percentile_result)){
    echo $percentile_row['user_id'].'<br />';
    $j++;
}
echo 'Total: '.$j.'<br />';
echo round(100/$j,1);

$players_worth = round(100/$j,1);

while($players_worth > 10){
    echo 'adding<br/>';
    $players_worth + $players_worth;
}

It seemed like a simple way to get it. It's just that the $players_worth + $players_worth; part isn't working when it's within the while loop. It works if I just echo it.

Or is there something I can add to the query that will make it select by a percentage? I have to do this for about 15 columns.

This is my existing query:

SELECT user_id FROM Players ORDER BY user_id DESC

Thank you for any tips you might have.

Edit:
I tried this, but no luck, when I var_dump it, it just says "bool(false)": MySQL: LIMIT by a percentage of the amount of records?

Answer 1

I got it and here's how I went about it:

First I got all the rows, then...

echo 'Total rows in table: '.$j.'<br />';

$twentyfive = floor($j*.25);
$fifteen = floor($j*.15);
$ten = floor($j*.1);


echo $ten.' '.$fifteen.' '.$twentyfive.'<br /><br />';


$topten=0;

while($topten < $ten && $percentile_row2 = mysql_fetch_array($percentile_result2)){

    $change =   "UPDATE Players SET " . $column['field'] ."=concat(" . $column['field'] . ",'%') WHERE user_id='" . $percentile_row2['user_id'] . "'";

    $wpdb->get_results($change);

    echo '<strong>in top 10%</strong> - '.$percentile_row2['field_1'].' - '.$percentile_row2['user_id'].'<br />';

$topten++;

}

And so on for the other percentiles. All the echoes were just to track it.

Answer 2

If you already know the number of records in the database, you could use LIMIT:

"SELECT user_id FROM Players ORDER BY user_id DESC LIMIT ".$rowCount*$percentage/100

I don't know of any way to use a percentage directly in a query, unless you already know the cutoff point for the value you're checking, which means you've already gone through the database and examined all the values.