MySQL junction table concatenation - mysql

Question

I have an requirement to return all educators associated with a session as a concatenated list, but to do it within a join (don't ask - I know there are multiple ways of doing it but I'm working with a library that won't accept those methods ;-))
I have a sessions table with session_id and session_name.
| session_id | session_name |
+------------+--------------+
| 1 | Swimming |
| 2 | Chess |
I have a session_educators table which is basically a junction table session_id and contact_id.
| session_id | contact_id |
+------------+------------+
| 1 | 1 |
| 1 | 2 |
| 2 | 3 |
| 2 | 4 |
I have a contacts table with contact_id and full_name
| contact_id | full_name |
+------------+--------------+
| 1 | Fred Bloggs |
| 2 | Mary Bloggs |
| 3 | Mark Smith |
| 4 | Shelly Smith |
So far this seems to be the closest I've come:
SELECT
sessions.session_id,
sessions.name,
educators.names
FROM
`sessions`
LEFT JOIN
(
SELECT
GROUP_CONCAT(contacts.full_name SEPARATOR ', ') as names
FROM
`contacts`
WHERE
contact_id
IN
(
SELECT
contact_id
FROM
session_educator
WHERE
session_educator.session_id = sessions.session_id
)
) `educators`
USING
(`session_id`)
But I'm really fumbling in the dark trying to figure it out, can anyone help?
What I'm wanting, as you can probably tell from the query, is a result like this:
| session_id | session_name | educators |
+------------+--------------+--------------------------+
| 1 | Swimming | Fred Bloggs, Mary Bloggs |
| 2 | Chess | Mark Smith, Shelly Smith |
Any help greatly appreciated - even if it's just to say it can't be done!

Answer 1

You shouldn't need subqueries for this. It is a few joins and an aggregation:
select s.session_id, s.session_name,
group_concat(e.name separator ', ') as educators
from sessions s left join
session_educators se
on se.session_id = s.session_id left join
educators e
on e.educator_id = se.educator_id
group by s.session_id;

Answer 2

I do believe you're making it all a little more complex than needed (unless I've missed something in your requirements? I know how much of a pain libraries can be...)
This worked for me:
SELECT
session_id,
session_name,
(
SELECT
GROUP_CONCAT(full_name SEPARATOR ', ') as names
FROM
contacts c,
session_educators se
WHERE
c.contact_id = se.contact_id
AND
se.session_id = s.session_id
)
FROM
sessions s
;