<?php
//Option 1
$sql = "SELECT id FROM schedule";
$result = $db->query($sql);

while ($row = $db->fetch_array_assoc($result)){
                $sql2 = "SELECT schedule_id, finish, points FROM results WHERE rider_id = 102 AND class_id = 1 AND schedule_id = ". $row['id'] ." ORDER BY schedule_id";
                $result2 = $db->query($sql2);
                while ($r2 = $db->fetch_array_assoc($result2)) {
                echo $row['id'] . "<br>";
                }
}
//Option 2
$sql = "SELECT schedule_id, finish, points, schedule.id
            FROM results
            LEFT JOIN schedule
            ON schedule.id = results.schedule_id
            WHERE rider_id = 102
            AND class_id = 1
            AND schedule_id = ". $row['id'] ."
            ORDER BY schedule_id";
$result = $db->query($sql);
while ($row = $db->fetch_array_assoc($result)) {
    echo $row['id'] . "<br>";
}