Misi gan numpang nanya lagi dong..

Hehehe..
Ini ane lg buat dashboardnya .
.tapi ko kenapa nilai nya selalu 0 ya??

<?php
$date = date('Y-m');
$query = "Select * from sales WHERE date LIKE '$date%'";

$result = mysqli_query($con, $query);
$revenue = 0;
If (mysqli_affected_rows($con) != 0) {
While ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
$revenue = $row['amount'] +$revenue;
}
}
echo $revenue;
?>

Mohon pencerahannya gann