db={"bookSchema":[{_id:ObjectId("637d05dc32428ed75ea08d09"),book_details:{book_name:"random123",book_auth:"Amber"},},{_id:ObjectId("637d0673ce0f17f6c473dee2"),book_details:{book_name:"random321",book_auth:"Amber"},},{_id:ObjectId("637d069a3d597c8458ebe4ec"),book_details:{book_name:"random676",book_auth:"Amber"},},{_id:ObjectId("637d06c05b32d503007bcb54"),book_details:{book_name:"random999",book_auth:"Saurav"},},]}

db.bookSchema.aggregate([{"$group":{"_id":{"$eq":["$book_details.book_auth","Amber"]},"score_ambr":{"$sum":1}},},{"$group":{"_id":{"$eq":["$book_details.book_auth","Saurav"]},"score_saurabh":{"$sum":1}},}])