Something

SELECT DISTINCT designation, reference,
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 1 
	THEN 1
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 2 
	THEN 2
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 3 
	THEN 3
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 4
	THEN 4
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 5 
	THEN 5
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 6
	THEN 6
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 7
	THEN 7
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 8
	THEN 8
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 9
	THEN 9
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 10
	THEN 10
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 11
	THEN 11
	END
),
count(
CASE WHEN EXTRACT(MONTH FROM date_sortie) = 12
	THEN 12
	END
),
count(sort.quantite), 
count(stock.quantite)
FROM magasin.sortie AS sort, magasin.produits AS prod, magasin.stock AS stock 
WHERE sort.num_produit = prod.num_produit 
AND stock.num_produit = prod.num_produit 
AND DATE_SORTIE > date_trunc('month', current_date) - interval '1 year' 
AND DATE_SORTIE < date_trunc('month', current_date) 
GROUP BY designation, reference