Need help again about joining tables

some context I asked a question about a MySQL request, my post can be found there: Need help about joining tables

Now I have another problem related to that, so on my page I'm listing tickets from a database my request is:

"SELECT
    glpi_tickets.id,
    glpi_tickets.name,
    GROUP_CONCAT(
            CASE WHEN glpi_tickets_users.type = 1 THEN 
            CONCAT(glpi_users.firstname, ' ', glpi_users.realname)
        END) AS creator,
    GROUP_CONCAT(
        CASE WHEN glpi_tickets_users.type = 1 THEN 
            CONCAT(glpi_tickets_users.users_id)
        END) AS creator_id,
    GROUP_CONCAT(
        CASE WHEN glpi_tickets_users.type = 2 THEN 
            CONCAT(glpi_users.firstname, ' ', glpi_users.realname)
        END) AS users,
    GROUP_CONCAT(
        CASE WHEN glpi_tickets_users.type = 2 THEN 
            CONCAT(glpi_tickets_users.users_id)
        END) AS users_id,
    glpi_tickets.date,
    glpi_tickets.priority,
    glpi_tickets.date_mod,
    glpi_itilcategories.completename,
    glpi_tickets.status,
    glpi_tickets.users_id_lastupdater,
    GROUP_CONCAT(
        CASE WHEN glpi_tickets.users_id_lastupdater = glpi_users.id THEN
            CONCAT(glpi_users.firstname, ' ', glpi_users.realname) 
        END SEPARATOR '<br>') AS last_updater,
    glpi_tickets.content
    FROM
        glpi_tickets
    JOIN glpi_tickets_users ON glpi_tickets_users.tickets_id = glpi_tickets.id
    JOIN glpi_users ON glpi_users.id = glpi_tickets_users.users_id
    JOIN glpi_itilcategories ON glpi_itilcategories.id = glpi_tickets.itilcategories_id
    GROUP BY
        glpi_tickets.id"

The result look like:

[ID][Title][creator][date created][priority][category][status][date modified][assigned to][last update by]
[125][helpdesk test][admin][29-01-2013 21:09][low][messaging][new][30-01-2013 17:52][Tony][admin]

For each ticket, creator - creator_id and users - users_id can contain multiple ID and name.

Now I want to display user information in another page, I used the same request but with WHERE glpi_users.id = ? getting the id from users.php?id=x

Everything works fine except the the creator and users, since the WHERE glpi_users.id = x only select one person.

I'd like a way to display then like in the previous request, thanks in advance

EDIT: Tried the GolezTrols solution but it's not working, here is my query:

"SELECT
                        glpi_tickets.id,
                        glpi_tickets.name,
                        GROUP_CONCAT(
                            CASE WHEN glpi_tickets_users.type = 1 THEN 
                                CONCAT(glpi_users.firstname, ' ', glpi_users.realname)
                            END) AS creator,
                        GROUP_CONCAT(
                            CASE WHEN glpi_tickets_users.type = 1 THEN 
                                CONCAT(glpi_tickets_users.users_id)
                            END) AS creator_id,
                        GROUP_CONCAT(
                            CASE WHEN glpi_tickets_users.type = 2 THEN 
                                CONCAT(glpi_users.firstname, ' ', glpi_users.realname)
                            END) AS users,
                        GROUP_CONCAT(
                            CASE WHEN glpi_tickets_users.type = 2 THEN 
                                CONCAT(glpi_tickets_users.users_id)
                            END) AS users_id,
                        glpi_tickets.date,
                        glpi_tickets.priority,
                        glpi_tickets.date_mod,
                        glpi_itilcategories.completename,
                        glpi_tickets.status,
                        glpi_tickets.users_id_lastupdater,
                        GROUP_CONCAT(
                            CASE WHEN glpi_tickets.users_id_lastupdater = glpi_users.id THEN
                                CONCAT(glpi_users.firstname, ' ', glpi_users.realname) 
                            END SEPARATOR '<br>') AS last_updater,
                        glpi_tickets.content
                    FROM
                        glpi_tickets
                        JOIN glpi_tickets_users ON glpi_tickets_users.tickets_id = glpi_tickets.id
                        JOIN glpi_users ON glpi_users.id = glpi_tickets_users.users_id
                        JOIN glpi_itilcategories ON glpi_itilcategories.id = glpi_tickets.itilcategories_id
                    WHERE
                       exists (
                            SELECT 
                              'x' 
                            FROM
                              glpi_tickets_users
                            WHERE
                            glpi_tickets_users.tickets_id = glpi_tickets.id AND
                            glpi_tickets_users.id = ? AND
                            glpi_tickets_users.type = 1)
                    GROUP BY
                        glpi_tickets.id"

Almost all the time it's showing no tickets at all, and sometimes it's showing a ticket but not related to the user, for example if I try users.php?id=1536 it will show the ticket number 789 that is created by the user 870 with user 1180 and 1632 in charge of this ticket...

Instead of filtering on an exact userid, you should check if the user is related to the issue, like this:

select
  t.title,
  group_concat(
    case when tu.type = 1 then 
      concat(u.firstname, ' ', u.lastname)
    end) as creator,
  t.priority,
  t.date,
  group_concat(
    case when tu.type = 2 then 
      concat(u.firstname, ' ', u.lastname)
    end SEPARATOR ' - ') as users
from
  tickets t
  inner join tickets_users tu on tu.ticketid = t.id
  inner join users u on u.id = tu.userid
where 
  exists (
    select 
      'x' 
    from 
      tickets_users tu2 
    where 
      tu2.ticketid = t.id and 
      tu2.userid = <youruserid> and 
      tu2.type = 1)
group by
  t.id;

For <youruserid> you can fill in the user id you want. This query will return all issues that are reported by that user (type = 1). But for all those issues, still all related users are returned, so your query result is still complete.