Database
[{"_id":1,"player":{"userId":"unique_1"},"total":100,"updatedAt":"2020-10-05"},{"_id":2,"player":{"userId":"unique_2"},"total":200,"updatedAt":"2020-10-05"},{"_id":3,"player":{"userId":"unique_2"},"total":200,"updatedAt":"2020-10-06"}]
Query
db.collection.aggregate([{$group:{_id:"$updatedAt",uniquePlayers:{$addToSet:"$player"},total:{$sum:"$total"}}},{$set:{uniquePlayers:{$size:"$uniquePlayers"}}}])