Getting the SUM in PDO

Question

Below is my code and for some reason it's not giving me the SUM. This always returns 0. Why doesn't it work?

I've used if ($totSubmits==''){ to avoid blank fields in my database.

I also tried removing AS due_fees and using $dueAmont = $result[0], but no luck though.

$sql= "SELECT SUM(dueFees) AS due_fees FROM coursePayments WHERE studentId = $student"; 
$stmt = $c->prepare($sql);
$stmt->execute();
$result = $stmt->fetch(PDO::FETCH_NUM);
$dueAmont = $result['due_fees']; 
if ($dueAmont==""){
    $dueAmont = '0';
}
echo $student." due amount ".$dueAmont;

Answer 1

fetch(PDO::FETCH_NUM)

Will not bring you an associative array back. That's a numerically indexed array hence you cant find your field.

PDO::FETCH_NUM: returns an array indexed by column number as returned in your result set, starting at column 0

Do

fetch(PDO::FETCH_ASSOC)

And that is

PDO::FETCH_ASSOC: returns an array indexed by column name as returned in your result set

That's what you need to get your alias back from.

Tip:

You can remove your if clause to check whether the value is blank and set it to 0.

$dueAmont = $result['due_fees']; 
if ($dueAmont==""){
    $dueAmont = '0';
}

Can simply be

$dueAmont = intval($result['due_fees']); 

Answer 2

Gah, use parameter binding! Also, fetchColumn() is nice and easy for single row / single column results

$sql= "SELECT SUM(dueFees) FROM coursePayments WHERE studentId = ?"; 
$stmt = $c->prepare($sql);
$stmt->execute(array($student));
$dueAmont = (int) $stmt->fetchColumn();

Addendum

When developing, always run your PHP environment with full error disclosure. Then you won't miss easy mistakes like in your code above. In php.ini

display_errors = On
error_reporting = E_ALL