Question

I have three tables in my database: reservations, events and users. I want to display all the users that subscribed to a certain event. The tables are linked via the following method:

SELECT users.u_name, events.e_id, events.e_title
FROM users
INNER JOIN reservations
ON reservations.r_s_id = users.u_id
INNER JOIN events
ON reservations.r_event_id = events.e_id

I need to join the reservation table because the field reservations.r_s_id correlates with the unique id of the user (users.u_id) and then the field reservations.r_event_id correlates with the unique id of the events (events.e_id). This was the only method i could come up with to approach all the necessary values.

It is my goal to get an output like below but have no clue how to achieve this

Event 1
 - user 1
 - user 3
 - user 9
Event 2
 - User 2
 - User 5
 - User 12

I tried using GROUP_CONCAT() and GROUP BY on events.e_title but that did not resulted the way i want it to

Anybody an idea?

Answer 1

Select from reservations, order the result set by events.e_id and print a new heading each time the event changes.

Like this:

$SQL = "SELECT users.u_name, events.e_id, events.e_title
FROM reservations
INNER JOIN events
ON reservations.r_event_id = events.e_id
INNER JOIN users
ON reservations.r_s_id = users.u_id
ORDER BY events.e_id";

$res = mysql_query($SQL);

$last_event = NULL;

while ($row = mysql_fetch_assoc($res)) {

    // check if curser moved to new event
    if (!$last_event || $last_event <> $row['e_id']) {

        // output heading for event
        echo $row['e_title'], '<br />', PHP_EOL;

        // remember ID of current event
        $last_event = $row['e_id'];
    }

    // output attendee
    echo '- ', $row['u_name'], '<br />', PHP_EOL;
}