[{"username":"root","passwords":["1234","root","123456"],},{"username":"admin","passwords":["1234","123456","admin","administrator"],},{"username":"root","passwords":["1234","root"],}]

db.collection.aggregate([{"$unwind":"$passwords"},{$group:{_id:{username:"$username",password:"$passwords"},count:{$sum:1}}},{$sort:{count:-1}}])