如何将页面中的所有行总计为sql LIMIT

i put limit in this code but how can i calculate the totalmin in this page?

here is my code

<?php
$id = $_GET['id'];
$sql = "SELECT * FROM time WHERE id = $id ORDER BY id DESC LIMIT 15";
$result = mysql_query($sql);
?>

<table border="0" style="width:50%">
<tr>
    <th>Time in</th>
    <th>Time Out</th>
  </tr>
<?php

while($row = mysql_fetch_array($result)){
echo "<tr>";
echo "<td><center>".$row['totalmin']."</center></td>";
echo "</tr>";
}
</table>

mysql_close();

i want to know how to total all the mins in 15 row with php code

Something like this may do the trick, if you want to show sum only But you should NOT use mysql_ functions, and this code is not sequre from SQL Injects

    $id = $_GET['id'];
    $sql = "SELECT * FROM time WHERE id = $id ORDER BY id DESC LIMIT 15";
    $result = mysql_query($sql);
    $sum = 0;
    $num = 0;
    ?>

    <table border="0" style="width:50%">
    <tr>
        <th>Time in</th>
        <th>Time Out</th>
      </tr>
    <?php

    while($row = mysql_fetch_array($result)){
        $num++;
        $sum += $row['totalmin'];
        echo "<tr>";
        echo "<td><center>".$row['totalmin']."</center></td>";
        echo "</tr>";
        if($num == 15){
            echo "<tr>";
            echo "<td><center>".$sum."</center></td>";
            echo "</tr>";
        }
    }
    ?>
</table>

<?php 
mysql_close();

You need to store $totalmin into your while loop and update it with new value if $row['totalmin'] is less then $totalmin.

Use something like this:

$totalmin = null;
while($row = mysql_fetch_array($result)) {
    if (is_null($totalmin) || $row['totalmin'] < $totalmin) {
        $totalmin = $row['totalmin'];
    }
    echo "<tr>";
    echo "<td><center>" . $totalmin . "</center></td>";
    echo "</tr>";
}    

Sum up the minutes as you loop through the result:

$sum = 0;
while($row = mysql_fetch_array($result)){
  $sum += floatval($row['totalmin']); //or intval()
  echo "<tr>";
  echo "<td><center>".$row['totalmin']."</center></td>";
  echo "</tr>";
}
echo $sum;

make sure you close your while loop