<?php
function resultToArray($result) {
    $rows = array();
    while($row = $result->fetch_assoc()) {
        $rows[] = $row;
    }
    echo json_encode($rows);
}
$mysqli = new mysqli("host", "user", "password", "db_to_use");
$email = $_GET['email'];
$query = ("SELECT * FROM Cards WHERE Email_FK='{$email}'");
$result = $mysqli->query($query);
$rows = resultToArray($result);
var_dump($rows);
//echo json_encode($rows);
$result->free();
?>