select * from figures
inner join figures_categorie on figures.categorie=figures_categorie.id
where categorie=1
 or categorie in
  (select id from figures_categorie as cat1 where cat1.parent=1
 or cat1.parent in
 (select id from figures_categorie as cat2 where cat2.parent=1)) ;

select * from figures
inner join figures_categorie on figures.categorie=figures_categorie.id
where categorie=1
 or categorie in
  (select id from figures_categorie as cat1 where cat1.parent=1
 or cat1.parent in (select id from cat1))