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db.collection.aggregate([{"$group":{"_id":"$itemNumber","ninetyDays":{"$sum":{"$cond":{"if":{"$and":[{"$gte":["$date",{"$subtract":["$$NOW",{"$multiply":[1000,3600,24,90]}]}]},{"$lt":["$date","$$NOW"]}]},"then":1,"else":0}}}}}])