您只能关联一个级别的深度。
采用：
SELECt m.nom, m.prenom, x.categories, y.areas FROM m3allens mLEFT JOIN (SELECt m2c.m3allem_id, GROUP_CONCAt(DISTINCT c.category_en) AS categories FROM CATEGORIES c JOIN m3allems_to_categories m2c ON m2c.category_id = c.id GROUP BY m2c.m3allem_id) x ON x.m3allem_id = m.idLEFT JOIN (SELECt m2a.m3allem_id, GROUP_CONCAt(DISTINCT a.area_en) AS areas FROM AREAS a JOIN m3allems_to_areas m2a ON m2a.area_id = a.id GROUP BY m2a.m3allem_id) y ON y.m3allem_id = m.id WHERe m.id = ?
