4 tables : client user carte and parrainage
table user got id_user as primary key. This is a foreign key for the 3 other tables

SELECT id_client, id_parrainage, user.id_user, id_carte
FROM `client` 
LEFT JOIN `user` ON `client`.id_user = user.id_user
LEFT JOIN `carte` ON `client`.id_user = carte.id_user
LEFT JOIN `parrainage` ON `client`.id_user = parrainage.id_parrain

result is (for a id_user):

13 NULL 35 NULL 
2 NULL 2 6 
3 NULL 3 3 
4 NULL 4 1 
4 NULL 4 2 
5 1 5 NULL 
6 15 6 44 
6 16 6 44 
6 15 6 42 
6 16 6 42 
9 NULL 15 NULL 
12 NULL 34 31 
1 NULL 1 4 
1 NULL 1 5 
1 NULL 1 32 
1 NULL 1 33 
19 NULL 45 NULL 




I got to count distinct id_parrainage (2 here)
and count distinct id_carte (2 here)