JOIN and GROUP_CONCAT with three tables

Question

I have three tables:

users:        sports:           user_sports:

id | name     id | name         id_user | id_sport | pref
---+--------  ---+------------           


        

Answer 1

Its not particularly difficult.

1. Join the three tables using the JOIN clause.
2. Use Group_concat on the fields you're interested in.
3. Don't forget the GROUP BY clause on the fields you're not concatenating or weird things will happen

SELECT u.id, 
       u.Name, 
       Group_concat(us.id_sport order by pref) sport_ids, 
       Group_concat(s.name order by pref)      sport_names 
FROM   users u 
       LEFT JOIN User_Sports us 
               ON u.id = us.id_user 
       LEFT  JOIN sports s 
               ON US.id_sport = s.id 
GROUP  BY u.id, 
          u.Name 

DEMO

Update LEFT JOIN for when the user doesn't have entries in User_Sports as per comments

Answer 2

I think this is just a simple join and aggregation:

select u.id, u.name, group_concat(s.name order by pref separator ',')
from user_sports us join
     users u
     on us.id_user = u.id join
     sports s
     on us.id_sport = s.id
group by u.id, u.name