select sum(s.lot_effectif),s.annee,s.mois from(
select *, extract(month from ope_date_debut) as mois,extract(year from ope_date_debut) as annee from  iav.vue_lot_ope_car where lot_tax_code='2055'
) as s
group by s.annee,s.mois
order by s.annee,s.mois