Database
[{"studentMcqs":[{"id":2024,"answer":"C","bookMarked":false,"mcqId":408041},{"id":2025,"answer":"B","bookMarked":false,"mcqId":408042},{"id":2026,"answer":"C","bookMarked":false,"mcqId":408043}],"mcqs":[{"id":408042,"answer":"C","mcqSubject":{"id":289,"name":"Mathematics","description":"Mathematics"}},{"id":408041,"answer":"C","mcqSubject":{"id":289,"name":"Mathematics","description":"Mathematics"}},{"id":408043,"answer":"C","mcqSubject":{"id":289,"name":"Chemistry","description":"Chemistry"}}]}]
Query
db.collection.aggregate([{$unwind:"$studentMcqs"},{$unwind:"$mcqs"},{$project:{mcqs:1,studentMcqs:1,mcq_comp_value:{$cmp:["$mcqs.id","$studentMcqs.mcqId"]},ans_comp_value:{$cmp:["$mcqs.answer","$studentMcqs.answer"]}}},{$match:{mcq_comp_value:{$eq:0}}},{$group:{_id:"$mcqs.mcqSubject.name",correctCount:{$sum:{$cond:[{$eq:["$ans_comp_value",0]},1,0]}}}}])