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):
Ids from
6 15 6 44 
6 16 6 44 
6 15 6 42 
6 16 6 42

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