DECLARE @Noeud int
DECLARE @DateFinPeriode datetime

SET @DateFinPeriode = '23/02/2010 15:32'

select * from Agent ag WHERE ag.DateCreation < @DateFinPeriode AND (ag.DateInactif > @DateFinPeriode OR ag.DateInactif IS NULL)

SET @Noeud = 1
WITH RechNoeud(PK_Noeud,FK_NoeudParent)
AS (
    SELECT n.PK_Noeud,n.FK_NoeudParent
    FROM Noeud n
    WHERE n.PK_Noeud = @Noeud
    UNION ALL
    SELECT n.PK_Noeud,n.FK_NoeudParent
    FROM Noeud n
    INNER JOIN RechNoeud r ON n.FK_NoeudParent = r.PK_Noeud
)
SELECT *
FROM Agent ag
INNER JOIN RechNoeud r ON (r.PK_Noeud = ag.FK_Noeud)
WHERE ag.DateCreation < @DateFinPeriode AND (ag.DateInactif > @DateFinPeriode OR ag.DateInactif IS NULL)