db={"transactions":[{"cashier":"1","deviceid":"P1","total":100},{"cashier":"2","deviceid":"P1","total":200},{"cashier":"1","deviceid":"P2","total":50}]}

db.transactions.aggregate([{$facet:{cashier:[{$group:{_id:"$cashier",cost:{$sum:"$total"}}}],deviceId:[{$group:{_id:"$deviceid",cost:{$sum:"$total"}}}]}}])