db={Demographics:[{"country_id":"BGD","country_name":"Bangladesh","population":"164700000","area":"148460","density":"1265"},{"country_id":"DEU","country_name":"Germany","population":"83200000","area":"357386","density":"232"}],statistics:[{"country_id":"DEU","dt":"2022-01-29","confirmed_cases":"2016684","deaths":"118335"},{"country_id":"DEU","dt":"2022-01-17","confirmed_cases":"53916","deaths":"143"},{"country_id":"BGD","dt":"2022-01-30","confirmed_cases":"12183","deaths":"34"},{"country_id":"BGD","dt":"2022-01-29","confirmed_cases":"10378","deaths":"21"}]}

db.statistics.aggregate([{"$lookup":{"from":"Demographics","localField":"country_id","foreignField":"country_id","as":"demographics"}},{$group:{_id:{country_id:"$country_id",dt:"$dt"},country:{$first:"$demographics"},maxQuantity:{$max:{$toInt:"$deaths"}}}},{"$sort":{maxQuantity:-1}},{$project:{_id:0,country_name:{$first:"$country.country_name"},dt:"$_id.dt",maxQuantity:"$maxQuantity"}}])