Combine information from 3 tables in one table (MySQL) - mysql

Question

I have three tables like this
couples
+----------+-------------+---------------+-----------------+
|couple_id | clubname | agegroup | group |
+----------+-------------+---------------+-----------------+
| 36 | club_1 | adults | C |
| 37 | club_2 | youth | A |
+----------+-------------+---------------+-----------------+
users:
+----------+-------------+---------------+
|couple_id | firstname | lastname |
+----------+-------------+---------------+
| 36 | andy | hort |
| 36 | katrin | wilson |
| 37 | hans | gertes |
| 37 | julia | menz |
+----------+-------------+---------------+
locations for training:
+----------+-------------+
|couple_id | location |
+----------+-------------+
| 36 | Paris |
| 37 | Berlin |
| 37 | Paris |
+----------+-------------+
The resulting table should look like this:
+---------+------------------------+--------+-----+----------------+
|couple_id| couple |agegroup|group|location |
+---------+------------------------+--------+-----+----------------+
| 36 |andy hort, katrin wilson| adults | C | Paris |
| 37 |hans gertes, julia menz | youth | A | Paris, Berlin |
+---------+------------------------+--------+-----+----------------+
Is there an elegant query to join these information in one query?

Answer 1

You should use group_concat with distinct:
select c.couple_id,
group_concat(distinct concat(u.firstname, " ", u.lastname)) couple,
c.agegroup,
c.groupd,
group_concat(distinct l.location) location
from couple c
join users u on c.couple_id = u.couple_id
join locations l on c.couple_id = l.couple_id
group by c.couple_id
If you have records in the couple table that may not exist in the users or locations table, then you may need to use an outer join instead.
#spencer7593 makes a great point -- you can move the aggregation to subqueries to include potential duplicates being removed by distinct:
select c.couple_id,
u.couple,
c.agegroup,
c.groupd,
l.location
from couple c
join (
select couple_id,
group_concat(concat(firstname, " ", lastname)) couple
from users
group by couple_id
) u on c.couple_id = u.couple_id
join (
select couple_id,
group_concat(location) location
from locations
group by couple_id
) l on c.couple_id = l.couple_id