Database
[{"collection":"bloodbank","count":100,"content":{"_id":{"type":"autoincrement","autoType":"int"},"bloodgroup":{"type":"enum","values":["A+","B+","O+","AB+","A-","B-","O-","AB-"],"randomOrder":true},"ml":{"type":"int","minInt":10,"maxInt":500}}}]
Query
db.bloodbank.aggregate([{"$match":{"bloodgroup":{"$in":["A+","B+","O+","AB+","A-","B-","O-","AB-"]}}},{"$group":{"_id":"$bloodgroup","total":{"$sum":"$ml"}}},{"$sort":{"_id":1}}])