Requête Sur trois Tables

Pas dans le groupe 2

SELECT C.*
FROM contact_group CG
LEFT JOIN contacts C ON C.id = CG.id_contact
WHERE CG.group_id <> 2

SELECT C.*
FROM contact_group CG
LEFT JOIN contacts C ON C.id = CG.id_contact
WHERE CG.group_id <> 2
 AND CG.group_id IS NOT NULL

Dans aucun groupe

SELECT C.*
FROM contacts C
LEFT JOIN contact_group CG ON C.id = CG.id_contact
WHERE CG.group_id  IS NULL

SELECT C.*
FROM contacts C
WHERE id NOT IN (
 SELECT DISTINCT id_contact
 FROM contact_group
) 

SELECT C.*
FROM contact_group CG
RIGHT JOIN contacts C ON C.id = CG.id_contact
WHERE CG.group_id <> 2
 OR CG.group_id IS NULL