Vous pouvez essayer avec having :
SELECT Ads.AdId
FROM Ads
JOIN AdsAmenities ON Ads.AdId = AdsAmenities.ads_AdId
WHERE AdsAmenities.amenities_AmenityId IN (2, 18, 1)
GROUP BY Ads.AdId
HAVING COUNT(distinct AdsAmenities.amenities_AmenityId) = 3
Dans le cas AdsAmenities.amenities_AmenityId les valeurs sont uniq, vous pouvez ignorer le distinct partie.