How do I Subtract Values of Multiple Queries - php

Question

I have had a long road to get to this last question. Everything is my code is working now, but I can't get this last little issue. Right now I have:
$sql = "SELECT phonenumber,email, dataplan AS currentplan, SUM(datamb) AS
value_sum FROM maindata GROUP BY phonenumber, dataplan";
$result = mysql_query($sql);
$row = mysql_fetch_assoc($result);
$val = $row["value_sum"];
$plan = $row["currentplan"];
$remain = $plan - $val;
if (!$result) {
echo "Could not successfully run query ($sql) from DB: " . mysql_error();
exit;
}
if (mysql_num_rows($result) == 0) {
echo "No rows found, nothing to print so am exiting";
exit;
}
It only subtracts the first value as opposed to the values for all. displayed like this:
while ($row = mysql_fetch_assoc($result)){
echo "<tr>";
echo "<td>".$row['phonenumber'] . "</td> ";
echo "<td>".$row['currentplan'] . "</td> ";
echo "<td>".ROUND ($row["value_sum"],2) . "MB</td> ";
echo "<td>".$remain . " MB</td> ";
echo "<td>".$row['email'] . "</td></tr>";
}
So my goal is to subtract all value_sums from all dataplans, but what I have now, gives me the first value for all columns. Thank you!

Answer 1

mysql_fetch_assoc() will always get one row. You can use it in loop, or better use PDO, eg. like this:
$sql = "SELECT phonenumber,email, dataplan AS currentplan, SUM(datamb) AS
value_sum FROM maindata GROUP BY phonenumber, dataplan";
$results = $pdo->query($sql);
You can read about creating PDO connections here http://www.php.net/manual/en/book.pdo.php