[{"_id":ObjectId("60509a82f5034f42e0e0f909"),"id":"zufferli-j","firstname":"Mark","middlename":"Clemens ","lastname":"Zufferli","works_in":"F","salary":99999999,"email_address":"addad@enron.com","avgjoin":[{"_id":"F","averagesalary":64833}]}]

db.collection.find({$expr:{$lt:["$salary",{$min:"$avgjoin.averagesalary"}]}})