Probleme avec COUNT() contenant une condition

Bonjour, je chercher a compter les valeurs qui sont comprises dans un interval :

Code:

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SELECT ville, COUNT(rempli_societe) AS saisi,
		COUNT(DATEDIFF(NOW(), depot) BETWEEN 7 AND 29) AS de7a29,
		COUNT(DATEDIFF(NOW(), depot) BETWEEN 30 AND 50) AS de30a50,
		COUNT(DATEDIFF(NOW(), depot)>50) AS plusde50,
		COUNT(*) AS total
	FROM communes, permis
	WHERE [jointures] AND DATEDIFF(NOW(), depot)>=7
	GROUP BY ville

Tous les COUNT comprenant les DATEDIFF me donnent tous le meme resultat.